First thing is to find out what it is he does that keeps breaking the machine. With that knowledge, one can then engineer proper reinforcement that will better last the particular user.
While installing larger bolts will work, I would not consider that in itself a proper fix. Making the bolts larger means weakening another part of the machine - specifically, at the bottom of the head where the bolts go through. Will this make much difference? Maybe, maybe not. Depends on what stresses this detector sees. So it's not just an all-around "you can do it this way" fix, but something tailored specifically for his needs.
I could fix it where it might likely never break again. However, just buried my Mom and have a hell of a lot of family stuff to do right now, as I have already explained to the OP.
In any case, it shouldn't be THAT difficult reinforcing the unit to provide additional strength.