It sounds like you have a problem that some farmers here have. They tile the low areas and divert the groundwater to a ditch, all underground. Have you consulted with a company that installs field tiles?
Like that idea, esp. if you don't really want a pond. They might do all that trenching and laying the tile for a fraction of the cost of a pond. Even if you had to cover the tile with more dirt, from an outside source, so it doesn't get pulled up. Then if you ever want a pond, you know exactly where to go to tap into a water source.
