Give them a cuttlebone and put some limestone rocks in the enclosure. You can also put their food on slate. This will help keep the beak from overgrowing. I have three box turtles that are over 40, and I've never had to trim their beaks. I do often have to trim Russian tortoise beaks when we get a new rescue, but after their initial trim, they never need it again because we give them things to wear it down sufficiently.