Wheel lockers - Advice needed

I have a '95 3/4 ton 4x4 GMC extended cab and do occasional off road
while geocaching.

Problems:

1st time - after crossing a small creek about 12 inches deep, front
unit went out, was electrical unit.
2nd time - steep section - had to hook up a jeep to pull me as I was
slipping around in the loose dirt/gravel
3 rd time - Slipped off outside edge of road avoiding a downhill
motorcycle that would not stop (next time he can go over the edge) had
to hook up to pull back on road, then when I got to next 4 point turn
that rose about 10 feet on the corner, lost traction.

Everyone else has been doing ok, the question came up about lockers on
the rear axel.

I know kind of what they do, but do they help a lot on a pickup like
mine?

Are there ones that are better than others?

Is the rear the best place to have installed?

About what does it run in $?