I'm glad I saw this post. We just got our boys last week and moved them into a bigger cage this weekend. The first cage was small and had only one small wire shelf so the only problem was the amount of waste in the bottom. ;-P The new cage has big wooden shelves and I noticed they were peeing on them. I had read this post before and remember the vinegar idea, so I have started wiping down the shelves and cage near them with vinegar, hoping to eliminate a problem before we have one with spraying. So thanks for the info!