Thems are some cute rats!

I haven't had the same issues as far as marking goes... I had mice briefly and caught them squirting between cages and it was enough to say "MICE GOTTA GO!!!!"

But one of my older males, doesn't do well with the other males, and is solitary when he's not breeding. He is waaaay competitive. And I did catch him once spraying another male.

But he is a black self, and I have heard others say that their black selves tend to be a bit harder to manage.

But if you aren't circulating them through the females, you shouldn't have any concerns with them.

Bruce