I have SMB in my small pond and I have placed areas around the edges with gravel. I selected the spawning beds for them. I have seen them swim around them and enjoy them. I did not place the gravel in tubs. There is some silt and otherwise that gets on the area but they dust that off as they prepare the beds. I hope this helps.

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1/10 - 1/4 acre pond plus 16 ft deep/ Plus 40 ft by 20 ft by 6 ft deep koi and fathead minnow pond next to it. Upstate NY