I had this problem just last week. I went to the local Forest
Service shooting range to take my boy to try out Grandad's
old Remington Model 4 22. I met a couple of guys there also shooting 22's.
One was kind of surly with having to share the
range. When they left, they locked the gate in such
a way using a Forest Service paddlock that my gun club padlock
wouldn't open the gate.

There I was with a young boy, a puppy, 95 degree weather, no
cell phone coverage and no other people around to let me out.

I could walk out, but it would have been a long, hot hike
and we were not "Equipped" for that.

But I alway carry one of those wire saws for metal and was
able to cut a link in the chain and drive home. I called the
Forest Service to let them know what I had done and that someone
with one of their keys was, well, not acting nice. The gate and
lock still functioned as ever because I only took out one link.
And the Forest Service was going to rig the system better so that
wouldn't be able to happen again.

As for fencing, in the parts of the country where I grew up
and range properties were measured in sections rather than
acres, it was considered okay when traveling by horseback to
take out the staples of the fence line enough to lower the
wire so your horse could cross, then you were to replace the
staples and leave everything as you found it. You
carried a fencing tool
(http://www.drillspot.com/products/337692/Crescent_193610CVSMN_Fence_Tool_Plier)
and some staples, with your horse.