Like Topsites idea as well as the marking paint.
One of the problems with flags (in general) is that no one removes them. Said company needs to do said work...Calls in for locates...Said work performed...Flags left to become a permenant fixture.
So, I pay attention to who calls in the locates and when the work is performed. Then I remove them.
"There is a class of people men, women and children, who must be killed or banished before you can hope for peace and order." William Sherman