Castrate who still thinks he's a stallion!?

I have 2 x 3yr old geldings, castrated over a year ago [according to the previous owners] and one is showing definite 'rig' like tendencies - particularly when any mares are around. It doesn't appear to matter if the mares are in season or not - this youngster will try and climb over gates, walls, etc to be with her/them!! The major problem is that our friends have 2 x 9 yr old mares and we would all like to go riding out together but the way this youngster is acting when a high fence is between them isn't encouraging. I don't think he's a cryptorchid but will get the vet to run blood tests to make sure. Are there any supplements on the market to ameliorate these tendencies and has anyone else experience in such cirstances? Thanks to everyone who gives genuine replies and yes, before anyone asks, I do know what Im doing!