Hi Chinook220,
The best way, is of course to approach the landowners. I believe in the up front and honest approach, that way the general public are much less likely to be persecuting us.
I've learned a method from someone ... fairly wise

(thanks Mr P), a great way to approach landowners.
Firstly, do not instantaneously blurt out the fact that you would like to practice bushcraft skills on their land. Again, there are common mis-conceptions about the things we do, and the type of people we are. Everyday day Farmer Giles or Lord Toff isn't going to know you from 'Adam' and doesn't really want drunken parties around a big fire in his woods.
Make the first approach by politely explaining that you are interested in local wildlife, and a keen wildlife photographer, and could you please spend some time photographing wildlife on a patch of land that he / she owns. Over time you should build up a good rapport with the person, and thus gain some element of trust. Then maybe after a while ask if it's ok to light a very small, contained fire to make a brew, and maybe a bacon buttie for lunch.
Eventually, you could try asking permission to STAY (not saying the word CAMP) overnight so as to observe nocturnal animals. Then .. hey presto, you've got yourself an overnight stay.
On top of this, you could eventually purvey the fact that you can carry out some woodland husbandry, and maybe add a little security to his land by just being there once in a while to stop people getting drunk and having a big fire!