We have a neutered male that tries to mark on occassion.....but the belly band and water bottle has 99% fixed that!
We have another one that "tried" to mark like that when we adopted him (older rescue dog), but he has hip dysplasia and fell over and tooted when he tried a couple of times, so he has quit too!
A friend of ours has a lab and I will tell you, it is really fun to watch him and our little ones play. They get along really well (of course I can't imagine anything not getting along with a lab).