bogydave said:
Just do it right.
Then no issues.
Bad advice. Accidents happen to even the most cautios and safety minded among us, that is a fact.
Best thing to do is probably to sign a waiver that limits your liability as well as that of the property owner. Spell out what you're doing, where and what the impact to the property is likely to be. Make sure to note that you're assuming your own liability for you personal well being and that you're not going to hold the property owner liable for your own carelessness.
No document can really stand up to scrutiny in court and pretty much any contract can be nullifed by a good attorney, but by spelling alot of it out and having both parties sign it, you cna feel a bit better and the property owner can rest a little easier too. If it came to it, a judge could read the document and see that both parties knew what they were getting into and can opt to throw out any frivilous suit.
The time I scrounged on someone else's property, I offered to sign a liability waiver that if I hurt myself with my saw or by lifting something too heavy that I wouldn't hold them responsible. I also stated that I wouldn't take my truck off their driveway and that I'd do my best to clean my mess up.