Ammonia isn't going to help - may actually make it worse. It may smell bad to you but to him it probably smells like another dog has peed there and he feels the need to re-mark his territory.
First things first - working with a 2 year old dog that may have some bad habits coming into your home. It is all about behavior modification.
1st step to the behavior modification is praise - tons and tons of praise when he goes go pee outside. Yelling, screaming, or worse is more detrimental to dogs than not doing anything at all.
Next part of the modification is that when he does pee on the bed foot, wipe it off quickly (good clean up later), take the rag or paper towel outside with him, and when he is sniffing it outside tell him he is a good boy. Again if/when he pees outside lots and lots of praise. Even leave those rags/paper towels outside for a few days.
Now the next thing needed done is to get rid of his pee scent totally - or the best that you can. I've found only one product that works which I am linking here called Nature's Miracle:
http://www.amazon.com/s/?ie=UTF8&key...l_9gm7eldxkc_b
Yes, kind of expensive but it does work. Until you can totally eliminate his pee smell from that foot it will be nearly impossible to modify his behavoir.
And being a male dog makes no difference - unless he is not neutered. If not neutered get that done ASAP.