Top critical review
Best solution has been to presoak collar
on February 3, 2017
Unfortunately not a silver bullet for preventing the collar ring. Found that to fully prevent a brown ring, I'd have to cover enough of the collar to clearly show the tape. I stopped using it after a week.
Best solution has been to presoak collar, scrub with a brush, soak in Oxiclean White Revive. Takes all the brown out.