to get your spells to have a higher DC you have to raise your base caster stat (wiz=int cleric=wis). the way the DC for a spell is determied is, i belive 1/2 caster lvl + spell lvl + state mod (wis,int,cha, whichever) + Feats. so if you wish to raise your dc for your spells, look at this formula and raise the parts you can to get a higher DC. For example, to get my DC up on my wizard, i cast fox cunning, that gets me an extra 1 or 2 points to the dc. for your cleric, cast owls wisdom to get your wis up higher.