Welcome to Pond Boss, and sorry to hear about this project not working out.

You may already know this, but before going into whether or not to get a liner, is there enough surrounding land to fill the .5 acre hole with water (from rainfall run-off), and is the grading done properly to guide water to the pond?

EDIT: I know you state that none of the water really flows to the pond. If that is the case, then a liner isn't going to help much.


Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."