When I was a new groomer, I HATED grooming difficult dogs. The wiggling frustrated me, the biting scared me, and I didn't yet have the tools to handle dogs that, for whatever reason, don't like to be groomed. It wasn't until I started my current job 4 years ago that I had the time and space to acquire the tools to handle the difficult dogs, and now, after 11 years of grooming, I actually seek out senior and difficult dogs. My favorite part of my job is figuring out how to make sure each dog has the best experience possible for their grooming.
It is my belief that in order to be truly comfortable grooming those difficult dogs, you need 3 things: time, patience, and experience. I can't help you find time or patience, but I can give you some tools that I believe can aid your experience level.
The biggest tip I can give you is to constantly pay attention to the dog's body language. With the possible exception of senile dogs, dogs don't bite for no reason. Usually they are biting out of fear or pain or even the memory of pain caused by a previous groomer, which I guess qualifies as fear. Once you figure out what a dog's trigger is, they are so much easier to handle.
Here are a few examples of dogs that had been labeled as difficult or aggressive that I have been able to work with and, in some cases, "rehabilitate."
My greatest success story is probably a Great Pyrenees that I've been grooming for over 3 years. The first time I met him, his owner told me that he had been muzzled by 4 previous groomers. One groomer had muzzled him for his feet, one for his butt, one for both, and one for the entire groom. That's interesting - usually dogs bite for the same thing every time they get groomed. What's going on?
The first time I groomed him, he was trying to climb out of the tub during the bath, which was a little frustrating but not a crisis because he was tethered. Since I wasn't sure how he would do for the blow dryer, I left him in the tub. As soon as I got near him with the dryer, he started doing what I call bite-barking. He was barking and snapping his jaws shut, but he wasn't aiming any bites at me; I was able to see that he was afraid of the dryer but didn't want to hurt me.
When I wash and dry a large hairy dog, I like to put in my ear buds with hearing protectors over them and listen to my favorite peppy music. Usually this is just to avoid boredom, but during loud and/or difficult dogs, it helps me to stay calm and tune out distractions. With my music going, I was able to stay calm and I dried him the best I could from an arm's length away. We don't have kennel dryers, so I just did the best I could with the velocity dryer.
Luckily I was able to coax the big guy up onto a table once he was as dry as I could get him. The first thing I do to (almost) every dog when they get on the table is nails. If you'll remember, feet is one thing he needed to be muzzled for previously, so I was cautious, but I wanted to give him a chance.
He was a little bit fussy for his feet and nails, but he never once tried to bite. Interesting.
On to shaving his butt sanitary area. When I went to pick up his tail and move it out of my way, he sat and turned in order to yank his tail out of my hands. Fascinating. Maybe I'll leave that for last and have somebody hold him while I shave that area. Brushing went well, even for his butt - as long as I didn't touch his tail. Brushing his tail was a fight but I managed it OK. I had somebody hold him up so I could shave his butt and he tried to get away but never snapped once.
All done and no need for a muzzle. Why didn't he snap at me when he had apparently snapped at 4 previous groomers? I believe it was a combination of things. Partly, I was able to stay calm and not get flustered by his bite-barking. Dogs are very sensitive to your energy; any groomer who's had usually good dogs act up when they are having a bad day can attest to that. By keeping my energy calm, he was able to stay calm.
Another thing that worked in my favor was not pushing him too far past his comfort zone. I uphold humanity over vanity above all and even extend that to: sometimes settling for "good enough" is exactly the right thing to do. I could have gotten that dog's head dry, but I would have lost any amount of trust he had developed in me, he would've gotten more stressed than necessary, and he would've been far crankier for the rest of the groom. I like to think long term - it was more important for me to earn his trust than to get his head dry.
These days, he doesn't bite-bark for the dryer any more. He'll even rest his head on my shoulder while I dry him, though he's starting to get spoiled and insist I scratch behind his ears any time I have a free hand while drying him. I can get his head most of the way dry. He even steps willingly into the tub and onto the table. He still doesn't like having his tail handled, so I handle it as little as possible. With a 120-pound dog, I think it's more important for him to like and trust me than to make sure his tail is brushed to fluffy perfection.
Now, I know some groomers will argue with my methods. Some groomers think it's better to force a dog through the things they don't like: "They have to learn to get used to it." I think in certain situations that method is warranted, particularly when dealing with puppies. But I don't think that's a one size fits all solution. After all, long term, if you force an already difficult dog through the things they don't like, they're just going to become more and more difficult and stressed. Stress can kill, so I try to avoid it as much as possible.
Another dog I have been working with is a Silky that had become so aggressive for his face that previous groomers were hardly able to trim it at all. He had a lot of pin mats in his overgrown beard, so I am assuming that he had a naturally sensitive face and groomers had been somewhat roughly brushing pin mats out of his face for most of his life, so he naturally associated the brush or anything else coming near his face with pain. Naturally, the solution for this particular dog is to stop brushing mats out of his face.
That first groom, even trying to cut the mats out of his face as gently as possible was difficult because he was afraid of ANYTHING near his face. After the first two or three times I groomed him, I gained his trust and he learned that I wasn't going to hurt him. I recently groomed him for about the sixth time, and while he kept his eyes squeezed shut and occasionally tried to keep his face away from me, he didn't even give me any "Elvis lips," much less snap at me.
I keep his face trimmed very short to prevent any mats and I use my thinning shears to cut out any mats that I do find, and he's actually become quite good for grooming. I still keep my guard up because he is still clearly fearful, but as time goes on and he trusts me more and more, he will relax even farther and become quite a pleasure to groom.
Many dogs are only difficult for one thing, such as nails. When this is the case, I try to save that one thing for last so that they aren't still upset over the one thing they hate while you are doing things they might otherwise cooperate for. Also, in dogs that hate having their nails done, I don't go for perfection. The longer you spend trying to get the nails as short as possible, the more stress you are going to cause the dog and the more they are going to hate it. Conversely, if you do the nails as fast as possible, they may learn to calm down a little bit because the calmer they are, the faster you can go, and the sooner the torture is over.
I have been grooming a Westie for nearly 4 years who used to be so difficult for her nails that it required 2 groomers wearing aprons and standing in the bathing room, then cleaning up the mess she had made before washing her (for any non-groomers reading this unsure what mess she was making, she would pee and/or poop every single time while trying to bite anything that got near her). Over the years, she has struggled less and less and less, to the point where I can now do her nails by myself at the end of the groom with her head well-tethered, and if she snaps at all, it is a half-hearted attempt meant to show her frustration rather than aiming to injure me. I attribute her improvement in large part to the fact that I don't spend forever trying to get her nails perfect, I just do one clip per nail and move on.
Sometimes dogs who were fine for grooming when they were younger develop issues in their older age. I go into much more detail on grooming senior dogs in this previous post. Some issues they might develop include "laziness" due to arthritis or hip dysplasia, fear biting when they start losing their sight, and dryer senility.
The key to grooming difficult dogs, in my opinion, is always trying to figure out WHY they are being difficult and how to best work around the problem. Remember: humanity over vanity, and sometimes good enough is perfect.
I hope I managed to help you at least a little bit. I'm sure I have more tips rolling around inside my skull but this post is already quite long. Feel free to comment with your own tips for grooming difficult dogs!