I agree with the bathyspheric map and electro shocking of the pond. Before you have the pond e-shocked, talk with them and get an idea what type of fishery you want. Then during the electro shock survey, any fish that you don't want in your pond can be removed.
I would have the mapping done first because if the pond isn't deep enough to support the fishery that you want, you might not want to do the e-shock survey and punt the property before sinking more $$$ into it.
