Should I limit my coupon by IP address or shipping address

Hi,

I have a promotion where the customer get a coupon when register.
I wonder, should I limit the coupon by IP address or shipping address?
Because if I limit by shipping address, they can change simple thing, like 781 Abc street, apt 2 to 781 ABC street, #2, and it would still work.
If I limit by IP address, would the customers using the same network (campus, company) get the coupon?