The "Unit - A unit comes within X of YOUR_UNIT" event is actually capable of detecting a "target", but only if YOUR_UNIT tries to attack the approaching unit. To sum it up, it is a combination of "A Unit is Attacked" event with its main purpose (detecting any unit within X range). I wouldn't go with this one for it triggering a trigger many times in a short time.
On the other hand, you can use this - if your unit attacks, of course:
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Events
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-------- Specific Unit Event --------
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Unit - YOUR_UNIT Acquires a target
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Conditions
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Actions
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-------- YOUR_UNIT = (Triggering Unit) --------
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-------- Target = (Targeted Unit)
This one won't spam-fire your triggers as much, but the downside is melee units not being able to target air units.
At last, you have what Marcos_M suggested, which is capable of detecting most units. However, I don't think you'd need such a small interval for it. Well, it really depends on the amount of existing Unbroken Rager units in your map. If you have a few of them at once, something around 0.4 timeout interval should be enough.
To be honest, the correct answer is: test them all and see which one suits you best, because having hundreds of registered units through specific-unit events in a trigger wouldn't be a smart choice either. Unless you know how to "recycle" your triggers.