We need a sticky some-where for seeking permissions...
Start with reviewing the metal detecting code of ethics.
TreasureNet - Guide
There are multiple threads scattered through this forum on the subject.
My take on it is just opinion of my own ,and partly from others ,your methods will evolve in time to suit you more specifically.
Smile when asking permission.
State your reason for asking. Perhaps " , my hobby is metal detecting , looking for coins and items from the past".
With modern shows on T.V. equating detecting to recoveries of treasure and high value objects , many of those who do not detect will suspect you are on to some great wealth hidden on their property and be suspicious of your intentions.
Some will ask what the most valuable thing(s) you recovered were ,others may be more concerned about you leaving holes or breaking pipes or bringing in a backhoe.
Only one permission asked for half the gold if I found a chest of it.
My reply was ,"sure but I get to keep the chest".
If a family heirloom was lost I'm more than willing to return it.
A plain silver coin of no note(not reworked into a love token or war souvenir, birth of a child ect.) before the hunt will go in a padded pill bottle.
I don't offer a cut or portion. That is up to whom ever grants me permission.
If the source wants to see my finds before I leave that's fine.
I offer anyone worried about holes a recovery demonstration. (Note ,practice recoveries till no sign exists of where you made a recovery fist!) Even on poor soils or yards, or on a back forty.
I'm looking for a coin older than I am ,that's a treasure in my estimation.
The odds of more are very slim ,but of course if some one put me in the way of a big windfall there would be an obligation to see that their life saw an improvement too.
My time ,tools, and knowledge are as valuable as your mechanic's to me. If your choice of a couple items when time for me to leave are not enough ,I may not be all that interested in your property.
If I don't know the value of a suspected high value item I will research it. Being not a real pirate it will work out and you will be involved in any great potential gain.
Where should I park? Do you want me to notify you when I leave? Can I return and hunt again or do you want a face to face request to hunt again?
Any thing lost in the past that is sentimental? (If so try to narrow down description of object and possible location).
A casual approach as an hobby enthusiast (not a treasure hunter) while smiling and not looking like a dog under a buffet table , helps get casual replies.
Dress presentably casual , enough to not look like a bum ..or an attorney.
Relax. The worst reply is a no , and that is not to be taken as personal. Imagine a knock at your own door and a request to look at your landscaping under the mulch for rare insects for instance. If you are prepared to take away the no's , and you can gain experience over time , by being honest and truly respecting others and their property, you'll get more permissions.
Some folks will wave you on with go ahead ,while others have concerns. Some are easier than others. Due to human differences.
An immaculate green lawn during a drought ,no need to ask , go to another site. Dry conditions and no rain in the very near forecast might mean no nice areas of ground cover should be cut...better to return anther time than kill spots in a nice yard, or noticeable areas of any yard..
A yard that looks like a bomb test range , go ahead and knock . Then assure the permission granter you will respect it. Honestly and mean it.
Let folks know you are a detectorist by hobby..they may know others with a lost item ,or a farm ect. that they think would allow you access.
Hello( with a smile.) "I'm so and so from such a place and I noticed your neat looking place has a decent age to it.
"This may seem odd but I metal detect as a hobby and am looking for properties with a little age to try and find a coin older than I am.
Mind if I take a swing at it?"
Let them list any terms or notes of importance and be prepared to remove any negatives.(Gets easier with time.)
"No! I don't want you diggin up my yard."
I can show you what a recovery looks like if you have any concerns about my leaving any evidence of being here besides my tracks.
My range is several inches in depth so I won't be uprooting your plumbing or anything crazy. When I get a signal I can check around it for a continuation that would indicate a buried shallow pipe or wire.
If still a No?
Always thank them for their time and have a super day.
If a yes ,consider a Christmas or anytime thank you card. Even if you found nothing of interest ,you are representing a polite group.