Hi Peter:
That is a very large area for a liner and will be expensive. If it is
seven feet deep and the soil is compacted it should be able to retain
sufficent level as a wildlife pond, depending the rainfall in your
area or if there is a natural spring feed.
I have purchased liners - for much smaller ponds- from Anjon Building
Products, Chesterfield, MO. and found them very good to deal with. The
best of luck!!!
Richard


http://www.anjonproducts.com/dave.htm