Every time my dog goes in to get groomed, he comes back looking nice, but he does something weird. He runs from one place to the next, and sits down really quickly. Then a little bit later, he runs to the next place across the room, and sits down quickly. I have heard that they get their anal glands emptied when they get groomed. Do you think that is why he is doing the sitting like he is? He also rubs his but on the floor a little when he sits. He is a Shih tzu and will be 5 years old next month.
I am a groomer and I can almost guarantee that it's because of the hygenic clip he's getting.
As for his anus getting nicked, sometimes it does happen when a dog is fighting and won't let the groomer get the clippers situated correctly for the cut. If it continues to be a problem, ask about it. There might be things you can do to train him not to wiggle. If it's razor burn, then get some mild lotion or neosporin and put it on the affected area, that should help clear up the irritation.