RE: Whitetail Institute "Extreme"
I've had good experience with Imperial CLover. Used it for many years. It needs heavy soil that holds moisture. Sandy clayalso seems to support good growth.The sand you're planting in probably dries out and the other issue is probably a fertility problem. If it's real sandy all the nutrients, required for plant development have been washed to deep in the soil for the plants root-system to reach them.
Soil test the area and check for N,P,K. If they are extremely low, that may be it, depending on how long it's been since you fertilized.
If the plants try to grow and then stop it's more than likely a problem with fertilitity, assuming the pH is correct.
The E#xtreme should work but you have to support the forage with nutrition, ie fertilizer. It may take mutiple applications each year to have success with anything.
Usually 2 oz of RU concrentrate at 41% per gallon is sufficient to kill off a field. Again the height and type plants can increase the %age. Use 17-20 gallons of water per acre.
Good Luck