1. use the construction horses and put tape between them
2. use cones (the larger the better) with a stake in the top hole and tape between them
3. fencing like they use at the NRC events at the start/finish area
4. use concrete blocks and depending upon what kind you use, you can either stick a stake in them, or you may need to fill the hole with some concrete and put the stake in them and let them dry. then tape between them
with either, you will probably need to spend some $$$
We've used 55 gallon drums at our event. The event is run at a horse show grounds so there's no shortage of barrels that we can use. The steel drums are heavy enough on their own to support tape and can be 20' or so apart. You could probably use plastic trash cans as well, but you might need some water or sand to give them eoungh weight to be stable.
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.