In a smaller pond a liner is probably the way to go. As you said Mikeyboy with little to no rain from May through October evaporation will take a toll. Dig the pond deep and plan on losing several feet of water during the course of a year.

JHAP
~~~~~~~~~~
"My mind is a raging torrent, flooded with rivulets of thought cascading into a waterfall of creative alternatives."
...Hedley Lamarr (that's Hedley not Hedy)