I work for a company that shoots professional fireworks and we have had the
same thing happen.
We go as far as to put up chain link fencing around the site and across the
trail and people still go around them. They either open the gates or crawl
over/around them because they don't think the fence is for them. We even put
up POLICE LINE tape (crime scene tape) and they go around or break it.
It has gotten to the point that we have police on site when we are setting
up and they STILL go around.
So I second the comments about the trail runners.