once the wolf takes the hill, he should work just as diligently to protect the hill. Dig trenches filled with water to drown those who approach. Barriers to entry should grow larger each day, as the pack of wolves trying to take the hill grows accordingly.
Introduce a pity sheep to the herd of starving wolves now and then, just to get them to kill each other to keep the numbers low.
Spread tales of how bad it really is at the top, and plant rumors of how the next hill is where all the glory truly lies.
Also, the spiked heads of the last wolves to approach the peak deliver a nice deterrent.