First off, Any zapper should work as effectively as any other. So here are your two options: 1. build one yourself. 2, buy one.
The zapper I use is a pretty good zapper. It costs $10.00 (unless you build it), is very small so you can keep it in your pocket and it's easier on the battery, here's the link http://zapperplans.com/ . Hope this helps.
God bless!