If I was going to bury a drain pipe cache on land that is not mine I would do it in the most public place I knew, like a park.

I would put on a pair of coveralls, my hard hat and boots.
Then I would go dig my hole, bury what I had to, cover it over and leave.
The more you look like a worker who belongs there the less interest you arouse.

You should note permanent landmarks you can sight on to locate your cache again. Things that line up like light posts and building corners are pretty good for establishing a line.

Be careful to cut the sod carefully so it grows back nice and even. If you don't the parks people might expose your cache when they try fixing the dead or uneven sod.