No problem! I hope you can figure it out. I've had many ideas for GPS-based games but as an avid gamer I couldn't help see all the ways I could cheat my own system.
Somewhat related... I'm not sure if you checked out my HN profile but I actually founded a gamification platform company called http://IActionable.com a few years ago. We started it before the word 'gamification' even existed got to watch in horror as people turned it into a cheap gimmick instead of properly implementing it. We actually don't like the term 'gamification' and the baggage that comes with it. Dealing with cheating was a high priority on our list when we initially targeted social applications but we eventually found the enterprise market to be the best fit for our technology. Basically, we were able to avoid the cheating problem because we made the 'game' involve people you really knew which naturally discouraged cheating.