I want to build or buy a green laser for camping & festival location

I frequently go camping at festivals or other large events. I have this idea that if I had a laser that shined straight up in the air I could use it as a beacon to find my spot and/or help other people find me. Some of these festivals are huge.

So......

My (tentative) goal is a laser in the 532-555 nm range. Ideally I'd like a small unit that is battery powered and will run for hours on a single battery. I am thinking a class 2 ( < 1 mw ) will be enough and keep it relatively safe. Naturally I would mount it high up to prevent curious people from looking directly in to the emitter.

I am handy with electronics, soldering, etc, I am mostly looking for general advise and even a recommendation on components.