I have been detecting for 35 years now. At first, I was very shy about asking permission. Through the years I have developed a line of BS (aka gregarious nature) by which I can talk with just about anyone. I am not shy much anymore. I am willing to spend a bit of time to gain trust. People are more willing to allow you to come on their property if they feel you are trustworthy. I also clean up trash, and show it to them before I cart it off. I have hunted all over the US, Mexico, Canada, and up into Alaska. I have been run off of a lot of places, but in the context of total numbers, I have been granted permission to hunt in some really great sites. Nowadays, I hunt, almost exclusively, older homesites, (1800's to early 1900's).
I worked with several historical societies through the years, offering my services to research sites for them, and providing detector services for the recovery and preservation of history. This has gotten me on many locations I would not have gotten on before.
Real Estate people are a good source as well for places to hunt. Get to know them, and they might gain you permission on some nice sites.
I have a business card, and I created the "North Texas Historical Council". It is a select group of people whom I hunt with who are members. You can see on the business card image below, how it looks. This has gained me a lot of traction when it comes to talking to people. I present myself as an investigator and preservation specialist. Says so on the card. I look for historical groups, geneology groups, local museums, and I talk to those folks, presenting my card, and explaining that I would like to hunt any areas they have knowledge of, with the intent to contribute relics to their collection. Those folks can grease the wheels to gain permission with older sites especially.
I also watch for scraped lots a lot in older parts of towns. Those are gold mines, and I seek permission from the owners. I talk to neighbors and get names. Then I contact the owners. Their lot is torn up already, and I offer to share if I find a treasure.
I keep organized information on sites I want to hunt, and go to the tax offices to find owners. I use an Apple IPhone for taking photos of holes dug and filled, showing how I work. BTW, that phone is absolutely awesome as a resource. I have look at google earth, topo maps, look up phone numbers, tax records, etc. BEST phone I have ever owned.
The key concept, at least imo, is credibility and presentation. I present myself as upbeat, humorous, yet professional. I get on a lot of properties. I have a liability release available at all times, and I am willing to sign it to get permission to hunt a lucrative property.
See any oldtimers? Years ago, Charlie Garrett stated in one of his early books, ask them if they know where any old timers are, and then proceed to gain knowledge of where to hunt, who to ask permission of, etc......
So, there you go, that is how I do it..........
HH
Dennis