This sort of thing.
It fastens onto your cock so that it hurts to get a hard on and it is impossible to wank or do anything other than piss with it.
You will still be required to suck your master and let him fuck you, but you your self can only get frustrated and tormented with no hope of satisfaction. Some masters freeze the key into a block of ice in the fridge, or put it at the bottom of a tin of paint, to make it awkward but not impossible to escape. Easiest way is to use a little combination lock that only your master is allowed to know the number for.
Welding in situ? if you do that you won't need a chastity device, you won't have any cock left to fasten it onto. Dont even think about it.