
Hello I now have beardies but have owned rough collies over the years I know what you mean about the knots alright!
have you tried chews I give mine a large dog chew the best ones that really get them engrossed are from tesco hartz chews theyre white in a wrapper they cost a bit more than in the pet shop but they love them and it works for me.
I put them on thier side and let them get started with thier chew then stroke them in the area that you are going to brush so that they get used to you touching them thier if theyre nervous the chew makes them forget what your doing then if you want to get it over with quickly cut into the knots and then gently tease them out otherwise you'll be at it tooo long and they become bored just do a bit then offer them a toy and take the treat away then try again a bit later giving them back the chew ....mine get excited when they see the chew bone come out cause eventhough they know thier getting groomed the chew mean more to them so they give in!!!!
obviously be careful when taking the chew away but as he is only a pup it just becomes routine.They'll hopefully let you carry on brushing them because the longer they get to eat thier treat!!
remember only to give that particiular chew for grooming!!!
EDIT: to add you could also put a slip lead on him so he cant run off,I would just sit on it.
HTH
~Roni