Do the hot wire. Rope will never keep them out. The thing is, I hope at some point the cows will be in a differant pasture in time for the deer to learn where the plot is. Otherwise it is a wasted effort to put the plot there. The fence will also keep the deer out, unless they learn to jump the hot wire which they can with little effort. Just think if they touch it 1st, they will want to stay away and find a food source elsewhere. Honestly I have done many foodplots, but have never done one where I needed to fence it to keep cows out.