A way prevent the "Excessive summoning wrath exploit"
You can gain unlimited piety without having to (O)ffer at altars
It is currently possible to pray repeatedly until your God is sufficiently angry to start summoning monsters (solars/holy slayers/greater daemons). This can be exploited if you can prevent the summoned monsters from reaching you (using for example the Unpick Axe to create walls around your character), and repeated praying at this level will eventually cause the character to gain excessive amounts of piety from the other two Gods the character isn't currently worshipping. My suggestion: When your piety level reaches an even lower threshold than the "summon monsters" one (which I think is at -20000 piety) the angry God stops summoning solars/holy slayers/greater daemons and instead shoots a death ray at the character. Even if you have resistance to death rays you'll still take considerable damage, so you can no longer keep on praying without dying.