I know how you feel. My boy was neutered last August (the same week he came home) and he is my only dog, yet I am extremely familiar with Mr Peeper. Just me coming home is enough to get Mr Peeper to salute. It's really uncomfortable for me since I wasn't expecting a neutered male to be so um... capable.
So I'm not surprised that your new boy actually locked, especially if it's soon after the neuter. He still has hormones inside of him driving this behavior. It seems like having your females spayed is out of the question, it sounds like you show. (I'm jealous!) Although it might hurt to separate from this wee one, it might in the very long run be for the best. I hope the belly bands help so you don't have to go down that route. Good luck!!