+1 for ultimates to get this spawner in the admin shop, with no option to /spawner just like the rabbit spawners.
No issue of gunpowder to go down too much anyway if the spawner is as the rabbit spawner - bit expensive say 50k per and as an ultimate only spawner. Ultimate does really need more items in its admin shop too and for something like this it'd be perfect.
Not all people know that this option even exists.
~ @Muunkee
Also, if they toggle explosions on to begin with, they'll know how to turn it off. Its the exact same command. If not then guess what, you'd have to have mobs toggled on the plot as well for any griefing to occur. Creepers are hostile mobs which require the toggling of mobs in towny owned plots :). In which case it is as Landonator419 put it, it is illegal to grief and lure. If you have any real concerns please inform us.