I think the problem is that the grass we use with them is young grass so not well-rooted so easy to pull out... I know that Candyce (on the SV Pets yahoogroup) uses a square of turf you buy at a garden store, she quarters it and plants each in a big pot...then rotates those in the house. I think then the grass has a chance to have decent roots so doesn't cause so much of a problem. I'm just not enough of a gardener to do that ;-)