How do you make it so that once you kill a unit, it will come back in the same location over and over again?

Constantly center a location on the unti and have the location check for that unit. If the unit is gone, then create another one of that unit.

Conditions:
[Player] brings exactly 0 [unit] to [checking location]

Actions:
Create 1 [unit] for [player]
Preserve Trigger.

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Conditions:
Always.

Actions:
Center location [location] for [player] on [unit].
Preserve Trigger.

I cant center location, i can only center view. Plus i want it so everytime a unit DIES it creates another one

Why can't you center location? Some editors call it "Move Location" also, so look again, and, that does work for each time a unit dies.

The action actually says 'move location' on the list, but when you click on it, the action text says 'center location'. Another thing to note is that, when you try to center a location on a unit, and it's not there, it moves the location to the center of the map.

EDIT: Just a little faster than me... You want to create the unit it the desired location as well.

Move the location to the unit, and every time there isn't that unit in the location, spawn him again.

Basically, what they said.

You could also do this:

C:
Player X suffers at least 1 death of Marine (for example).
A:
Create 1 Marine at 'Respawn' for Player X.
Set Deaths: Set to 0 of Marine for Player X.
Preserve trigger.

That's for if you only want one Marine at a time on the map.
If you want more than one, just change the set deaths action:

C:
Player X suffers at least 1 death of Marine.
A:
Create 1 Marine at 'Respawn' for Player X.
Set Deaths: Subtract 1 of Marine for Player X.
Preserve trigger.

Note this will not work if you kill the Unit with triggers. Otherwise, it's a really simple reliable method.