Custom magic item help?

[Pinkie Pyro]

I was reading the rules for custom magic item creation, and I didn't see anything relating to what a continual item does if the spell it uses is instantaneous. IE: you want to enchant a rock so that it continually casts shocking grasp, and deals 5d6 damage when it touches an enemy, or perhaps you want to use cure minor wounds/ repair minor damage to heal you or a construct 1 HP/per round.

As I can see it, the spell would be re-cast every round, for it to count as continuous, is there anything by RAW clarifying this?

[TuggyNE]

It would probably just be a use-activated item, not continuous. Same price though.

[theIrkin]

Like the above poster said, it would be easier to say it was use activated. In the shocking grasp example given, it makes more sense as the stone goes off every time it is touched by a sentient being, or every time it's moved (once per round), etc.