I have found there are many simple things that can work well for an existing pond. I have used wood spools the electric company has their line on. My local electric company gave me all I wanted for free and I just picked them up with my trailer.
I read an article in pond boss suggesting pallets, (stacked with cinder blocks between 3-4), as good for cover and a bonus was that fathead minnows lay their eggs on the underside of the wood. I set those up in at several depths and the shallows. Small baitfish seem to like them. THE SPOOLS though are the ticket to me. They are heavier duty and come in many sizes which is great for different depths. The wood is good for fatheads and the bass love them especially in the summer.
They can lay underneath the top and it is cooler.
We have had unbelievable success catching fish on every one!
I found the best way to put them in is just float them out to where you want it--- I buy several different lenghts of steel fence posts (for different depths), and drive it down the middle with a sledge hammer so it is about 4' in the pond bottom and sticking up about 1' above the water (so I know where it is).
I then place cinder blocks around the base and on the top. She sinks right to the bottom. I have also placed 2-3 together and run nice size heavy horizontal logs across the top (secured).
I try and place a long brush pile near them thinking the bass will hang out at the spool nearby and pick off bait fish off the brush pile. Just a thought, it is working well for this guy in Oklahoma! Good Fishing!