Electrical tape is probably the best product to use, as duct tape tends to slip if it is not put on expertly, which sometimes even experts don't do...
Of course, with larger specimens, you would use more wraps of the tape. Be sure to pull the tape taut to stretch it as you wrap it. The tape is not meant to stick to the gator's snout, but rather to stick to itself.
If you're a really robust and experienced handler, you can do this alone with a specimen up to about 8 feet long or so. This involves everything Bill mentioned, in addition to holding the head properly after 'setting' it, and then carefully and quickly wrapping the tape - this method takes practice and a knowlege of the gator's ability to laterally swipe its head.
For a more aggressive gator being wrapped solo, you would have to pull its head back and under your chin, minimizing the power of the neck muscles, and wrap the tape as you keep the head back. I do NOT recommend this to a beginner (!!), but if you are working toward being an expert, it is something to consider reaching for, with practice and someone to spot you. One should not really be dealing with that size crocodilian without a 'back-up' person present,anyway, in case of an emergency.
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Israel Dupont
Winter Haven, FL