My understanding is that WH leaves seeds around and keeps spreading and coming back. I'm not convinced a ring can really confine it?
At least here in The South, WH is too scary and illegal to use in a decent sized pond. (Class B misdemeanor in Texas for possession.)
4 acre pond 32 ft deep within East Texas (Livingston) timber ranch. Filled (to the top of an almost finished dam) by Hurricane Harvey 9/17. Stocked with FHM, CNBG, RES 10/17. Added 35lbs RSC 3/18. 400 N LMB fingerlings 6/18
