I think am going to try solid concrete block maybe, 4" x 6" x 16", with a hole drilled in them just large enough to fit the steel spike from plastic step in posts we use on the rest of the course. Maybe set them 12' apart.

Thanks

4 foot high crowd control free standing fencing is best option.
Try calling some local event folks to see if they have access to any of those.

Otherwise I have seen people use the Highway road barrels with the heavy rubber bases and stretch either tape or snow fencing between them.

Either way, if your worried about crowds entering and exiting give them an access way that is marked and manned so they don't go jumping in at the wrong spot.

I borrow these from my local Parks Dept. They are tall, the heavy bases keep them upright, and you can run tape across their tops.

Website I found this image from called it a Delineator Post. I call them candle cones.