If it's a skin head, take a piece of hihe from a broken head and wet it; this will cause it to stretch. While it's still damp, attach it over the slit with HIDE glue.As the skin dries, it will pull the slit together.

troll

p.s. the razor blade does work. the head is slackened and there is the added advantage that the Bodhran cannot be played.

pax

troll