Help! Ive just bought the Chartwell from Home & Roost for my guinea pigs to have more space as they are quite big males but the ramp is too slippery for them. They cannot get up or down it without skidding and falling and I'm worried they will hurt themselves. They are now refusing to go near it. How can I make it non slip for them? Sand Paper? But how to get it on as cant use glue in the cage. Please has anyone else had this problem?