more specifically this is for the U-Bolt type bike locks.
the cable ones, you can usually just wrap around the seatpost,
but the U-bolt are a little more difficult to carry around while your biking.
this can be built for around $3.50 (less if you already have some of the parts) and take about 10 minutes.
Step 1: Materials and Tools
-one foot section of PVC (for my lock i used 1 1/4" pipe, but it may ne different for your lock)
-2 hose clamps
-3/4" drill bit
-clamp (not required, but helpful)
Step 2: Marking your PVC
i marked both ends to be cut, since they didn't cut it straight at the hardware store.
Step 3: Cut your PVC
if is very helpful to hay a vice, or a clamp.
you also want to use a saw that has relitively small teeth.
i prefer a hand saw over an electric because it allows me to work slower and make less mistakes.
Step 4: Mark the PVC for holes
and mark where the holes in the lock are.
for this, you'll have to have the lock open.
you could simply make the pvc short enough for the lock to go through,
and then you wouldn't even need holes.
however i opted to drill holes so that the lock wouldn't swing back and forth.