Help for Matting under Arms

[Allyson, Peri & Taquito]

I searched around for this specific question, but was unable to find.
Does anyone have tips for successful brushing/combing of the arm area (especially UNDER the arms)? Peri is over 9 months and is starting that matting stage. I brush her DAILY, but noticed yesterday some pretty fierce matts under the arms. They are so incredibly hard to get out and Peri whimpers when I gently brush them....even with DH holding her. All-in-all, she doesn't mind grooming - I think she thinks it's a game and she gets treats.
But how do I tackle the arms? She does NOT like it one bit and this is the main place she matts right now. I use a Les Poochs brush that works quite well all around.
Help! I am trying to be diligent with brushing every day so as to avoid shaving.....

[Nancy, Ned, Clancy, and Charlie]

Ned is groomed and I think she cuts this area and the belly areas very short, but since we have had him groomed since he was 4 months old, I actually don't know if he is naturally shorter there or not. He hasn't ever had an underarm or tummy mat so I suspect it is shorter. My DH cradles Ned in a baby position on his back so that I can get the underarms and tummy. The matting starts overnight! You do need to comb also.

[Allyson, Peri & Taquito]

I cut out 5 huge matts this weekend - behind ears and arms. I was able to comb out a few around the belly area and near the tail. Wow - this really did start overnight!!!!

[Nancy, Ned, Clancy, and Charlie]

Allyson, remember you can use a product like Cowboy Magic to help comb out mats and if you need to cut them out, slice through them sideways in several places and then brush/comb and you can usually salvage some of the hair.

[Barb @ Gemstone Labradoodles]

I think you mean slice in the direction of hair growth :-)

[Nancy, Ned, Clancy, and Charlie]

Yes, the scissors are never pointed toward the doodle's skin. I always just assume someone would know what I mean, but I shouldn't assume. I am old and what is logical to me from dealing with kids and dogs may not be to someone who isn't.

[Nancy, Ned, Clancy, and Charlie]

Brushing Ned has always been a 2-person job for us. Luckily for Ned (or for us), my husband and I team groom. Ned actually falls asleep.

[Lucy & AnnaBelle's Mom]

Has anyone else ever heard that the black (darker) dogs are more tolerant of the brushing mats than the cream/white dogs. Someone asked me this one day and I had never thought about it, but it is definitely true at my house. Lucy literally goes to sleep if I let her lay down, but Sophie is on top of every more I make and if I even think about hitting a tangle she lets me know. Good thing she is the easy one to brush out!

[Nancy, Ned, Clancy, and Charlie]

Apricot Ned goes to sleep in my DH's arms but he would not settle down if he were not force held.