I knock doors every single weekend, 98% of my hunting is done at old farm houses where I just knock and ask, here is how I do it, and I have this memorized and say the exact same thing every time
knock, knock.....lol

good morning, my name is Terry and I have a hobby of metal detecting. I enjoy searching around yards like yours for old coins, tokens, buttons etc.
I was driving by noticed your house and was wondering if you minded if I detected your yard.
nine out of ten times, they say "sure go ahead" and away I go. Seldom they might ask stuff like how will you get the item from the ground, then I explain I will cut a horseshoe shaped plug flip it back, retreive the item then flip the plug right back.
I NEVER EVER use the word "DIG" to a homeowner, I always say cut a plug and retreive the item.
sometimes they might act interested and ask things like, what do you normally find? do you sell your finds etc.......
I explain to them almost all old farm yards will have wheat pennies, indian pennies, sometimes silver dimes, various relics, such as buttons, tokens, etc.
and I also say that I never sell my finds, this is a hobby, and not a money making adventure.
but I'd venture to say 80% of the people who give me permission just say sure go ahead and that is the end of the talk, they close the door, and I start detecting.
It is extrememly easy, as I said I do it every weekend.
