Hmm it's been a while since I've had a chance to fish a nice pond for largemouth, but here's what I'd do. Poppers during low light periods at sunrise and sunset. I like big deer hair bugs or frog imitations. Try two different retrieves - either pop it, then let it sit for a loooong time until all the ripples subside, then pop it again; or swim it across the surface with a steady pop, pop, pop, pop. It varies on which retrieve they want on any given day. Try the slow method first, and if that doesn't get a response, speed it up.
When the sun gets up a little higher, switch to an intermediate line and strip big streamers around the bank, deep water spots in the pond, or any cover. Bluegill imitations or a long black rabbit fur strip that looks like a small snake or salamander would be a good choice.
If that doesn't work either, find a fly that you can bounce along the bottom like a jig. A magnum superbugger is a good choice. Example here:
http://www.feather-craft.com/wecs.php?store=feacraft&action=display&target=JF408It's got enough weight to get down to the bottom and it rides hook-up so it doesn't snag as much. Crawl it very slowly across the bottom in a series of short hops, trying to imitate a crawfish scuttling along.
If none of that works, go fish for bluegill instead.
bd