It the owner of the garage had to move it, then they would have to move it in accordance with current building codes in that state.That's called an encroachment and if it's been there for a statutory period (15 years here), the owner of the encroaching structure (garage/fence) may assert a right to the effected land on the basis of adverse possession (called: title by prescription). If the owner of the garage/fence cannot claim adverse possission, you could strike up a deal to sell the propery effected by the encroachment (if you own it, otherwise the mortgage holder has to approve the deal) or bring action against said encroacher to have the fence removed on the grounds of trespass.
Check out your state's RE laws because they vary from state to state.
I always thought that with encroachment, the offending individual would have to move back 5 yards.