Speaking from a really longterm idealized answer, the answer is "both". You should communicate to the students that you take several measures to make cheating

Speaking from a really longterm idealized answer, the answer is "both". You should communicate to the students that you take several measures to make cheating difficult like passing out multiple versions of the same exam. You should also mention that you're consistently inconsistent. Sometimes you have 4 exam kinds, sometimes just 2. You do your best to mention it, but you know, people forget things. Forgive an unkind analogy, but when you're training a dog you don't want to reward it _every_ time. You actually want to be inconsistent with rewards so that it doesn't intentionally stop the behavior the first time it doesn't get a reward. The goal is to train students to not cheat by communicating that the cost of cheating is very high. At the same time, actually hunting down possible cheaters is hopefully not valuable - there's always some freeloaders but they should be at a low enough percentage to not influence very much.