How to mark out courses?

I know fell races traditionally aren't marked out at all. However the one we organise in the South West, the Wild Night Run, is. The problem we're running into is how to mark out races. Actually the Wild Night Run isn't too bad because we using reflective poles and flashing lights to supplement the arrows. But daytime races are a nightmare! The Dartmoor National Parks Authority is not keen on spray chalk. We used plastic tape tied to reflective poles in the past. But we have a farmer who's dead against the tape and the poles on their own are hard to spot in heather, gorse etc. Flour & sawdust often won't last the 24 hours or so between marking the course and running on it & also get trodden away before the back-markers get there. Does anyone have any bright ideas on how to mark out daytime fell races in a cow and sheep friendly way?

http://www.newitts.com/product/PACK-...qyAaArJH8P8HAQ

I use a combination of tape and these flags. I have laminated A4 signs sometimes at key points such as a path junction.
If you are following tracks, you don't need to flag all the way, just around the path junctions.

These work well and are very cheap and easy to carry

http://www.nhbs.com/title/186069/mar...HLkaAnCL8P8HAQ

Handy if there is not a well defined path.