A Mark to round....
Our club used to use a small Danforth or similar fluke anchor, with about 6 feet of chain, and then a rode length appropriate to the depth. We would also put a length of chain or a coffee can of concrete about 6 feet under the mark to make the initial part of the "tether" hang straight down in our 2 - 3 kt river current. That kept most keels from fouling the mark.
When you get tired of re-inflating and patching the bladders in the spendy "racing marks", do what we did and instead use Really Large (!) teardrop-shaped bright orange fenders. Indestructable.
Retrieval note: you throw a loop of line over the "fender marks" to lasso them easily....
My experiences, FWIW,
Loren in PDX