My 9 year old rabbit has gotten into the habit of digging in his litter. He is having a problem of a watery eye. I am sure it is from his digging. I took him to the vet and she could find nothing wrong. She flushed out his eye and the problem went away, but it keeps happening. I think he gets stuff in his eye when he digs. Any ideas on where I could get a scatter proof litter box?