Veils are basically nothing else than blocks against perception.
Protection against scrying, i.e. divination, is simply a straight up block against divination.
Consuming a use everytime someone tries to scry for you is a bit of a judgement call. Usually veils are not reactive, like defensive items are when defending against physical attacks. You have to activate them in order to make use of them.
But the benefit the item offers is rather specific, so personally I'd allow a reactive setup.
Maybe restrict it in a way that the item cannot be turned off. So even if someone who you'd want to find you looks for you, they have to get past the block to do so. Unless you actually take off the item of course.
If the character has an item base strength of 10/4, then two slots get either an 11/4 or an 10/6 item. I'd go with 11/4, since thaumaturgic divination can get to higher shift values pretty quickly.
Anyways, power 10-11 gets you pretty nice protection against most quick tracking spells. Harry's standard tracking spell for example would have trouble to find you. But if the tracker takes his time to do a little prep-work, he'd probably be able to find you anyways.
