Gotcha Gecko

A crocodile or alligator. Reference to a lizard (simp. Gecko) that grabs you from underwater.

The tourist was taken by a gotcha gecko when they were swimming in the waterhole.
There are too many gotcha gecko's in the water traps on the golf course to retrieve your ball.
Don't fall out of the boat. There are too many gotcha geckos.

or something

An object used (other than a rock) to lean a Flameless Ration Heater (FRH) against in order to heat a Meal Ready to Eat (MRE).

"What do I lean my FRH on to heat my MRE?"
"Read the instructions. It says to lean it on a rock or something."