Geocaching may sound like great fun, sending the kids out cycling to discover the countryside, but if done in a haphazard fashion by a naive individual it could be a disaster and I can see all sorts of liability issues. Woodlands would appear to be a favourite location, because by their nature they conceal the object and there are more places to hide it.
Suppose someone pushes through my hedge without consent and places a cache in the wood, and a couple of local 8 year olds come out cycling to try and find it. Firstly, you're half a mile away from the nearest house so if you get into trouble its a long way for a rescue party and there are no distinct landmarks.
So here are the two little scamps having a great time scrabbling round my wood. Unfortunately they dont know that one area still has a large number of broken bottles in the undergrowth left by the travellers. There are also various bits of wire in the ground to trip over and the odd snapped branch making a nice stake to impale yourself on(I did that one myself as a kid), and theres the odd bicycle part, car bit and metal sheeting protruding from the ground. Trip or fall on one of those and it could be a serious injury. My log heaps are large, loose, and not designed to be climbed on, if they rolled, you could get crushed. Maybe the cache is inside a log heap? There are those interesting blue berries on the plants on the roadway. Why not see what they taste like? One single berry will kill you (honestly); its deadly nightshade and I've several growing wild in the wood. I've also found a nice greeney white mushroom, its a destroying angel, one bite will kill you. And if it rained heavily over the previous couple of days, I get a couple of feet of water in the bottom of the very slippery old clay pits, enough to drown a child. Sometimes I have the embers of a fire still smouldering and might have forgotten to take the fuel can home, what happens if we put some on the fire? Theres a tractor going along the outside of the hedge doing something, shall we go and have a look? Whats the big whirring thingy coming towards us?
If any harm comes to these adventurers, I suppose its me that's liable? Maybe I was negligent putting up a sign 'private' because these kids aren't British and can't read English? If they are Eastern European, 'privet' is Russian for "Nice to see you!".