Dome of magical protection

The caster conjures a protective dome with a range of 15ft centered around him.

Any spell below the level the dome is cast and any magical magical projectile get blocked, but force the caster of the dome to make a concentration roll to keep it alive.

Spells above the level of the dome (and any projectiles affected by such spells) force their own caster to make  a check with their spellcasting ability competing with the caster of the domes concentration.
If both rolls are equal, the spell goes through the dome, but it isnt ended.
If the defender rolls higher they block the attacking spell but need to roll another concentration check.
If the attacker rolls higher their spell shatters the dome, causing the defender xD6 psychic damage (x being the difference between the attacking spell and the dome)


If the dome is cast on a level above 1 the area that is protected increases by 10 feet per spell level.