Personally I don't think zipties are much protection. Any pocketknife will defeat them.

My solution is, rather than buying expensive bike lights, to buy cheap but incredibly powerful small flashlights, and attach them to my handlebars with interlocking hose clamps, tightened by wrench (for security and also to eliminate rattling). My light is the same as this one, you can also find kits that include one or two batteries and a charger. The biggest cost component of lights like that is the battery, so expect a cheap kit to include a crappy battery. You can get a good battery for under $10, I got a pair of these to rotate between. A full charge will give me a week of commutes.