welcome to PB victor.
as i dont have experience with liners specifically for pond building, it would be good to have some follow-on advice from others, that said, some red flags went up reading your post.
in leaky soils, and spending the $$ to seal with liner, i would not risk puncturing the liner with rocks/boulders placed directly on liner. you might be able to CAREFULLY install a soil bed beneath each boulder you want to place, but keep in mind that boulders with irregular surfaces will have their weight distributed on the sharp edges, and water is extremely heavy. if the slightest tear occurs, water will find its way through, and yer pond will leak.
