You just have to be vigilant - but there is no way to prevent EVERYTHING from happening. We travel quite a bit and there is nothing grosser than the grass around gas stations/rest stops. Yet, my baby HAS to go potty. I try to watch ALL THE TIME but it is nearly impossible and they can see things down in the grass that we can't see and they are lightening quick when they want something.
As long as Kirby (love the name, by the way) has his shots, and takes heart gard - then he is about as protected as he can get. And of course, he has you watching out for him too - don't beat yourself up - we can only do as much as humanly possible to keep them safe - but we just can't keep them in a bubble.
Good luck with your guy - he sure is a cutie!!!