Grooming issues can arise for several reasons. The dog may have had a bad experience at a grooming parlour, may have been roughly handled as a pup, may be body sensitive due to injury or disease or may simply be unaccustomed to being touched over every part of his body. As behaviours are linked, dogs that have grooming issues may also find containment difficult (which includes being on a lead or wearing a harness or dog coat), and usually dislike being towel dried. They may also be timid or defensive around strangers and other dogs and fearful of being examined by a vet.
Keep each session short and do not try to achieve too much in one go. Several short sessions are going to be far more effective than one long session.
Ensure that you watch your dogs responses at all times and if your dog is concerned about being touched on a certain part of his body, go back to the places where hand contact was more acceptable. Build your dogs confidence over a few short sessions and try to stop the session before your dog indicates that he has had enough. It can be extremely tempting to keep working to see how far you can go but if you can work below the threshold at which your dog has to react you will gain his trust more quickly and help him to learn that grooming can be a pleasant experience.
If your dog is concerned by direct hand contact you can cover your hand with a large, thermal sock or a sheepskin mitt. This is an important step for dogs that dislike being groomed even if they are not worried about being touched as it helps them to change any negative associations they may have with grooming brushes. You can also try a soft, rubber brush such as a jelly scrubber which are often more acceptable for dogs that are worried by brushes. Small heated pads such as hand warmers placed inside socks to ensure that they do not burn the dog can also be of use to relax the soft tissue. Again you will need to ensure that you do not catch his coat with any of the tools as this will obviously reinforce his fears about being groomed.
Remember you can mark all calm responses with treats.
Build slowly over several sessions until your dog is happy to be handled all over his body. You can use the jelly scrubber and/or sheepskin mitt to alternate between circular touches and slow sweeping slides over his body to accustom him to the sensation of being brushed. Again make sure that you aren’t going to be pulling on matted hair.
If you need to trim out knots before brushing, and If he has been worried about scissors in the past, break it down into easy steps. Stroke him all over with the handles of the scissors as you did with the paintbrush, feather etc. Tape up the sharp ends and stroke him with the blades as well. Progress to working on one matt at a time, doing the round hair circling the hair, then snipping out the knot and remember to breathe when you are working with your dog. Holding your breath or rushing will cause tension in your hand which will concern him.
You may also need to invest in new grooming equipment. Hard brushes and combs can be extremely uncomfortable for some dogs particularly as they age and this can be where the problem started. Even if you do need to use slightly firmer brushes, alternate between grooming your dog and doing slow touches with your hand or the mitt or jelly scrubber rather than trying to brush him all over his body in one go. Breaking a grooming session down in this way is likely to be far less threatening and therefore far more acceptable.