Hmm..my boy has only ever had one behind his ear and that was because I was a wicked slacker that month. Otherwise, he just doesn't seem to mat that easily. My girl I need to use thinning shears behind the ears to prevent them and I do use a spray detangler with a fine toothed slicker once each week. Thinning out with wide angle shears really works well to prevent them in the first place and still leaves the dog looking natural without any cut lines or scissor marks.
