No one has asked what is behind the wall that your spicket comes out
of. If you are on a concrete slab and the spicket is on a wall that is
not open on the other side (i.e. adjacent to a finished room) it isn't
exactly going to be simple to add a turn of valve. If you have a crawl
space, I don't understand why you woudln't have a shut off inside.
Either way, you should weatherproof outdoor spickets, especially in
areas where the temperature frequently drops below freezing.

Get your spicket fixed/tightened, if possible have a shut off valve
installed, and for safe measure you can purchase an insulator from your
local home store (Lowes or Home Depot) which is basically a styrofoam
cone that fits over the spicket .