I'm not a relic collector, I don't even own a metal detector but I've done a bit of detecting with others in Normandy, Holland, and in the Bulge around Bastogne, and west of Grandmenil.

First of all it is a bit dicey, technically you can get in trouble if you get caught trespassing or using a metal detector in many places throughout Europe. If someone wants to throw the book at you and make life difficult they can.

I know of someone who was actually shot at by a French farmer last June in Normandy. He admits he should not have been there (he had asked for permission a few days before but was denied, he pressed his luck a few days later. I guess he laughs about it now but...).

Along those lines though, there are many people who spoil it for others; they'll trespass, and dig up a field (or a yard!) and not replace anything, or leave garbage...you can see why some folks get upset.

With that said, If I'm going to be on someone's land I'm always sure to ask permission, and go with a local person in case things get complicated.

But that is only half the battle, successful metal detecting requires a bit of skill and acumen in trying to determine where certain positions may have been. (It isn't always how it was depicted in the history books either) In some ways it helps to think like a squad leader in assessing the terrain and looking for obvious areas of approach or defensive positions.
A lot of times by finding the remains of fox holes, gun positions, or command dug outs, ammo from both sides etc. you can put together a pretty good picture of the movement of the battle.

I've found a lot of bullets, fuses, casings, ammo cans and things like that on WW2 battlefields, but a lot of places have been picked clean for the big ticket items so finding an MG42 in a hedgerow is less than likely these days.

But finding things in the ground wasn't the only way to come across those items. For years farmers had picked up things on the battlefield and put them in their barns, collectors know where to go to find them. A bunch of farmers have some amazing things (parachutes, Medical bags, musette bags, mines, unexploded grenades, rifles you name it) they'll show you if they like you. A few years ago I was with a friend who had a tip about an abandoned farm in Normandy just above Carentan. I accompanied him to the barn, and right inside the door were 3 Gerry cans in good condition. (He left them--it isn't really easy to bring a gas can, or 3 on a plane back to the states.:-)

There was a well on the farm, rumor had it that the surrendering Germans who had occupied the farm were forced to drop all their weapons down the well, we didn't get to find out if that were true or not, maybe someday.

More recently, just off the 501st DZ in Normandy a line of stables was being refurbished to be part of a B&B, in the attic of the stable they found a heathy cache of US and German weapons, ammo and other things, all in pristine shape presumably left there since June of '44. So it pays to have people in the know.

Last month a WW2 vet was in Bastogne, a guide took him to what the vet was was pretty sure was one of his old foxholes. They dug up some unspent .30 cal ball ammo that the vet was pretty sure he dropped in December of 44. What the vet didn't know is that you can't put that in your carry on bag, so when he got to the airport in Amsterdam they stopped him. It took some smooth talking and an understanding security chief to let him keep his bullets.

Interesting topic to say the least.