Killing coral (on purpose)

[asylumdown]

Just sold a large colony of hydnophora, but it left behind some encrusted base. I won't be able to put anything else in that spot until it's all dead (that stuff is agro!). I can't take the rock out as it's the base of a larger structure, so what's easiest/most effective - epoxy, kalk paste, peroxide, etc.?