Grover is a take-charge kind of dog, he seems to think that the only opinion that counts is his. When it comes to grooming, he has no problem letting you know it just isn't his thing. In fact, he might even become a bit aggressive when you approach him with the brush and clippers. You could, of course, secure him in place and put a muzzle on him, so he can't bite you. But, this will never teach him to kick back and enjoy being groomed. Instead, you need to teach him to stay calm and relax at grooming time.
Just because Grover is a bit on the dominant side, doesn’t mean you have to let him get away with it. If Grover is a bit on the aggressive side, it could mean he has had a bad grooming experience at some time in the past. Your job then will be to help him come to see grooming as a good thing and that it is okay to kick back and enjoy it.
Just because Grover thinks he is the boss, once you make him understand he is mistaken, grooming should become a time to relax and for both of you to enjoy a little bonding. Take your time, let Grover set the pace and it won't be long before he is coming to you to be groomed on grooming day.