why do rabbits pee on each other

i've had harvey for about 3 years i got ralph in january (both male rabbits) their pens are next to eachother because i thought it would be nice for them to see/smell eachother through the trellis. what a mistake. now that ralph is fully grown, he can jump over the (vertical 4ft) trellis into harvey's pen, i wouldn't mind so much if they didn't get up to naughty activities
and, if that isn't bad enough, they now urinate on eachother which is even more grim because they are both white i am having to bath them every other day. what can i do to stop them? are my rabbits homosexual or do they all do this? they are definately both male. i know you'll probably say to build a higher fence or seperate their pens, but in my garden, it just isn't possible. i've tried letting one out to run around leaving the other in his cage then swapping them round but i don't think it's very fair on them. please don't say they need neutered, my bank account is still coming to terms with yesterdays shock withdrawal for the cats treatment. anyway, i'm all out of ideas. still can't work out why they like to wee on eachother.

Belle aka female rabbit just humped on my other rabbit's head (Romeo) and peed on him.

This is my first time to see that.

I'm sure it already happened few times when I wasn't paying attention or wasn't in the same room. That would explain why there were stiffed fur on Romeo's head. Like if she assume that I give treat to Romeo.

She will come to Romeo and hump him. I always push Belle off Romeo's head/back. Today, Belle thought I am about to give treat but I didn't. I just want to pet Romeo (Belle don't like to be touched). So Belle came to Romeo and humped him. Romeo didn't bother to move. AND I didn't bother to gently push Belle away. I thought it would be nice to know if they did actually have fight while I wasn't in the room.

Then Belle hopped away. Romeo came after her and asked for groom. while there's pee stain on his head. That's how I discovered for the first time. Mind you, they are already fixed and have been together for TWO years. But why pee on head? I didn't find anything from google search.