Course Marking

For temp marks that last a few weeks, spray chalk. 
Can looks like spray paint, applies like spray paint, and will last through a few rains, but in a month or two will be gone.  
I have used it to mark start line where city did not want me to spray one across the street. Blue seems to be bright for a few days then fade well into the tarmac.

Perhaps it depends on the brand of spray chalk, but whatever the spray that others have used around here isn't much different than paint. There was one race in our local park where the organizers put down huge, obnoxious,  course markings all over the park including on some decorative stamped concrete road crossings. The marks were still visible after a year! If you decide to use this stuff you might want to do a few test marks to check that the particular brand you are using will actually disappear after a short time.

The color of the spray chalk tends to define how long it lasts as much, maybe more, than the brand (must be some pigments are more persistent than others). Pink tends to fade within a few weeks, but I've seen green marks still visible after 10 months, which included a particularly harsh New England winter.

I like mag nails and sometimes with washers. 

Sure the snow plows can remove the nails but using mag nails with a larger diameter than concrete nails tend to leave a scar in the asphalt.

The best way is to document well and I take perspective photos for use in locating marks.

We chip out a little blacktop such that the nail head is below the road surface.

guidobrothers posted:

We chip out a little blacktop such that the nail head is below the road surface.

Wow.

Oscar - your mention of the NPS billing Bob Thurston leaped out to me reading through this thread again:

One of my other "lives" is that of a competitive rules official for another national (sport) governing body. The NPS apparently doesn't take too kindly to any sort of encroachment, or at least not without getting their fair share of the "pound of flesh."

A particular event organizer was informed that they would NOT be able to have their triathlon bike leg go out onto a stretch of the Gulf Islands National Seashore, forcing them to double back on a three-mile stretch of their bicycle leg. Two-lane road...1,200 athletes...what could possibly go wrong?

While the flora and fauna were most likely not irritated by the incursion of human triathletes onto their front yard, it placed some major safety/fairness concerns in the hands of the CRO's working the event.