Sorry needed to add...
It is almost impossible to sex crappie 100% correctly...all you need is 1 mistake and your pond is shot!
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Best snag proof cover is pvc...it will also last almost forever. The only drawback is it is not biodegradable and offers nothing back into the beginning food chain for the zooplankton, etc.
You can put wood limbs in the middle and pvc on the outside, or do the milk crate stacks with wood in it...I would build pvc buckets and then drop wood "laydowns" around it.