Fleece Sudden chewing problems

[Itsjess555]

Nessa and Lily have been on fleece for several months. I have had no problems with it until a couple weeks ago when I went to do the weekly fleece change and noticed a lovely hole had been chewed in it. I was a bit perplexed because they had never even attempted to chew on it before. And this week I noticed another, slightly smaller hole. Of course, they only do it on my favorite fleece So has anyone else had this problem? If so, did you manage to solve it or get it under control? I really want to stick with fleece because it is way cheaper than the paper shavings I was using before. Thanks!