Niina! Yeah, oh well! He started doing it when he got the bladder problem, probably pure frustration! He did it about 1 meter from his litter box.

4 feline house! Thanks! The second and third one seem like a good option and quite easy to build. At the moment, we've got some logs of wood in our yard, will check if one of them is tall enough. Putting sisal around is also a good idea!

AmberLee! The one you posted is definately tall enough!! I'd love to see if Fister can climb all the way up - I bet he can! I realize that the bottom of it has to be pretty wide not to tip over!