It could be tied to their salary. It could be a 3 strikes policy. Something they care about should be put on the line when they sign a warrant. If they get it wrong and the warrant was frivolous, they lose something. If they get it right, and the search produces exactly what they predicted, then they get something. Judges would very quickly turn away investigators with insufficient evidence. It would also produce some very wealthy judges who would be worthy of their title according to an objective measure. The best judges would be the wealthiest.
Needless to say, they shouldn't be presiding over the trial, which determines whether the warrant produces a guilty verdict.