Hear is a neat and easy way to make a bike lock holder that stays on your bike.
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

You will need
-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

tools:
-saw
-sharpie
-3/4" drill bit
-drill
-clamp (not required, but helpful)

Step 2: Marking Your PVC

hold your PVC pipe under your lock and mark how long it is with your sharpie.
i marked both ends to be cut, since they didn't cut it straight at the hardware store.

Step 3: Cut Your PVC

Next you will cut the 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

Next, hold your PVC under your lock again,
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.

Step 5: Drilling Holes in Your PVC

Next, drill the two 3/4" holes in the pvc.

Step 6: Check to Make Sure Your Lock Fits

Before putting the lock on the bike, make sure it fts in the PVC.

Step 7: Attaching the Holder to the Bike

Next use your two hose clamps to attache the holder tot he bike.
i wrapped elecrical tape around my tube, so i wouldn't scratch the paint.
to use, simply unlock the lock and use it.