Tips for fishing deeper

[brushhog]

We haven't had much luck this last month trying to fish a little deeper. Anybody want to share their ideas? The ponds will be in range in size from 4.5 acres down to about 1.5. Depth maxs out at about 18-20 feet with 8-12 being normal water is stained, pretty murky. The bottom structure is hard to guess at in the deeper parts.. we've hung up alot when c-rigging plastics though. I've tried some deep diving cranks, but don't think i'm very good with them. Any ideas would be appreciated. I could answer any other questions about the ponds if more info is needed. We don't have any problem catching smaller fish along the shore, in structure and cover, but the big boys of spring/early summer seem to be missing? We'll be in a boat mostly, but shore ideas are welcome too!