Hey FETMO, We've all been there. I got one buddy that still won't help me put brush out after I almost drug him out the back of the boat with a huge tree drapped across the boat. Persimmons make good tops. They are dense and naturally heavy and takes very little weight to sink. I only use the ones that are about as long as my 16 foot boat now for easier handling.
Try this next time...Tie the butt of the tree to the front of the boat and the tip to the rear. Take two 5 gallon buckets with lids filled with rocks and attached to about a 3 to 4 foot piece of nylon rope, solid copper house wiring, or some other fastener. Have the buckets in the boat where you can tie them to the base and about 2/3 up the tree. When over your drop point, untie the tree and just flip the buckets over the side. I like to take a hole saw and drill a large hole in the middle of the tops to help them fill with water quicker. Personally, I remove the handles and wire thru holes drilled in the side of the buckets. I don't want to get hung on the handles plus I believe that the handles might rust away too soon.
This is what works best for me now.

Dave