I've got riprap 100% around the small pond and on the levee of the large one. I personally like it but it does have it's drawbacks. I can't say it's much of a growth preventer specific to cattails/willows/etc, at least not after year 3 or 4. Eventually the rock settles and you get growth. Even with landscaping cloth underneath. I used landscape cloth on the levee of the big pond and hand placed the rock. It stayed put but it's now showing some vegetative growth.

I put mine there to help prevent washing out of the bank from wave action. In that area it has worked exactly as intended.

It's a lot of work and expense depending on how you place it and what your source is but I wish I had more of it personally.

Dale

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"When tempted to fight fire with fire, remember that the Fire Department usually uses water." - anonymous