1) make it a portable item instead, or make a shrine someplace, attuned with a portable item that serves as a 'conduit' for the prayer. You still need to find a secure place for it, but that could make for some interesting RP with the indebted villagers.
2)For one, I don't suppose the soul of the slain dragon is eager to serve you. Add a 'must win it over' complication, in exchange for extra power. just an idea.