When State Farm started cancelling homeowners policies in Florida, we went looking for new insurance. To get it, we had to take the diving board off our swimming pool, otherwise we could not get insurance. It's the same with trampolines. I'll bet it's the same with self-built dirt bike jumps.
Laws and insurance rules vary significantly between states. The only person who can give you an answer to your question about waivers you can rely on is a lawyer in your state. I also expect that your homeowners insurer will be very, very unhappy, waivers or not. You very well may be told that waivers will not protect you, and your insurance will not cover you.
The trouble with squirtdad's response is as follows: If a kid gets hurt, he's going to need care, and possibly expensive care. Whether the kid belongs to a neighbor who you know and is not likely to sue isn't the point. Their health insurance (or Medicaid, depending on their circumstances) is going to have to pay. Regardless of whether the parents want to sue, their health insurer may look to you or your homeowners insurance for subrogation. Health insurers get a lien against a 3d party who may be responsible for an injury, and regardless of whether the insured (the kid's parents) want to sue, if they want their insurance to pay for the injured kid's care, their insurer might go after you.
Last edited by Kurt Erlenbach; 03-09-10 at 07:05 PM.