One easy solution to druid buffs overwriting it is to just buff-block the druid buffs. There's really no need for us to be using druid buffs
If cleric symbol is overwriting Oathbound Protector, then there's something wrong, because it should be blocking it.
Oathbound Protector (Rk1) has:
Stacking: Block new spell if slot 3 is effect 'Max Hitpoints' and < 2014
Kaerra's Mark (Rk3) has:
3: Increase Max Hitpoints by 1989
Even Oathbound Protector Rk. I *should* be blocking Kaerra's Mark Rk. III... is it not working like that?