There are wire cutters, as you used, and there are cable cutters.

Cable cutters as below with a scissor action will slice through cable locks like string.
Take your 1/4" cable to a bike mechanic and ask him to cut it with his park or shimano cable cutters.

Also "industrial strength" bolt cutters do not get dull by chopping tree branches (). My bolt cutters were purchased by my Grandfather in the late 1950s and they still work perfectly. They have an unusual double lever action and are barely over a foot long and have been used to rescue friends who have lost their keys on a number of occasions.

Just because you don't have the tools, does not mean that thieves don't. Anybody with elementary metalworking skills is going to be able to bust your lock faster than you can open it with the key.