Freelance web developers: how do you handle the build up of maintenance work?

One problem freelance web developers face is that alot of times the client will want a maintenance contract. If you build enough websites and agree to maintain some or all of them, eventually you could hit a point where you can't take on any new work because you're doing maintenance all the time. How do you guys solve this problem? Outsource the maintenance somewhere? Stop taking on new work? Something else? Thanks!