Good luck with you permission. Hope it happens.
Not sure if you told him the details of exactly why you wanted to be there, but I try to keep it as vague as possible. I once tried to get permission for an old cemetery by a creek (Relax all you anti-cemetary people.... there is more to the story) Apparently, this cemetery was around in the mid 1800's and kept getting flooded, so they exhumed all the bodies and moved them to another cemetery across town and sold off the land. When I told the owner all the details, he thought it was awesome and seemed totally fine with it. I had a buddy coming up who had actually done the research so when I got an actual date for the hunt, i stopped by again and was avoided like the plauge. He was home, and I talked to his kid, but couldn't get permission. tried several times over the next month or so, and even saw him hide behind the staircase once so he didn't have to face me.
Learned 2 things that day:
1) tell the owner what you need to tell him to warrant you asking to hunt his property but try not to make it sound like some amazing spot or they will think your going to find gold coins everywhere.
2) be ready to hunt when you ask so they don't change their mind later.
Good luck with what sounds like a killer site.