My 10yr old border collie has taken to wetting on my sons bed, even thou we are in he doesn't ask to go out. This has happened 3 times, could he be jealous of the kitten we brought into the house 8 months ago, or could it be a medical problem? He only ever does this on my sons bed never anywhere else in the house.

I'm guessing that since he doesn't do this anywhere else it isn't medical, but keep an eye on him just in case. Male dogs usually do this to mark their territory. Was he neutered when he was a pup? They say that neutering a dog causes them to mark there territory less.

I don't think he's jealous of the new kitten I just think that he is showing her that that bed is his and not to touch. Animals can be very territorial and they mark their territory in order to make others understand not to touch it. This sounds more like a territorial behavior and not a problem in relation with age or jealousy. Below is a website that will hopefully help you and your dog.
http://www.dogchatforum.com/dog-marking-inside.htm:cool: