Tips on getting rid of / preventing matted fur

Does anybody have tips on how to prevent / get rid of little balls of matted fur on your sib? He’s brushed every 2-3 days and deshedded every 2-3 weeks, but still get small clumps of matted fur under his forearms where it’s especially hard to reach.

Any tips on how to cut those off - I’ve tried with a small scissors but he absolutely hates the process and will try to bite and scratch me, or how to prevent them from happening? He’s going to a groomer next week so I’m not too concerned about that for now but would like tips for future maintenance!