Answer: The best solution for the long-term is to patiently train the dogs to go elsewhere. Or, you could install at least a temporary physical barrier. In the short-term, repellents would seem to be the only solution. There are a number of commercial products available (Hinder or Ropel), but they do need to be applied and reapplied according to the label instructions in order to be effective. Most large garden centers stock a variety of them or try Gardener's Supply Company (www.gardeners.com). Perhaps one or another will work for you.
Here is a recipe for a home-made dog repellent which is intended to keep them from digging but might help in this case. Unfortunately it sounds rather smelly.
Mix into a quart of water: one clove garlic (chopped), one onion (chopped), 1 teaspoon Tabasco sauce, 1 Tablespoon cayenne pepper or chili powder, 1/2 teaspoon dishwashing liquid. Dribble around the area to be protected (don't get it on the plants themselves). Be sure to wear rubber gloves and be careful not to get this in your eyes or on your skin.
I have one other thought. Is it possible that they are marking the area because of another animal nearby? Thanks for writing and good luck!
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