Start by using a repellent like Bonide Mole Max (it also works for gophers). This is a castor oil-based repellent that is not harmful to animals or birds. Take extra care to apply more heavily around holes. This granular formula is easier to apply than a liquid spray. Apply the repellent gradually towards the direction you want them to leave the property, in other words, leave them a way to get out. Applying the repellent to the whole space at once will just “trap” them there. If it is really very bad, you might consider a gopher removal/trapping service such as Smith’s Pest Management which focuses on trapping over poisoning.
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