possibility?

is a passive taunt ability possible without doing an every so often trigger (lag issues).

Passive Taunt... well, there are a few ways to think about going about this, depending on exactly what results you want.

Firstly, if you don't want to use an interval trigger, you can have a trigger that fires whenever an enemy unit comes within a certain range of the Tuant Aura creature, the action of which would be to order the entering creature to attack the creature with the Taunt Aura.

However, that would only fire once for each creature, when they come in range. Also, in large battles it will be firing quite often, although it won't be nearly enough to cause a lag issue. You may want to add something that causes a visual effect on the Taunted units, just so that players will know which things are under that effect. You'd have to make such a special effect disappear whenever the unit is ordered to do anything else, though.

Alternatively, having the unit gain the Taunt ability, use it, and lose it, every second or every couple seconds would not be a particularly laggy trigger, both because the interval is rather generous and because the actions of the trigger would be so few.

For something like this, there are undoubtedly other solutions as well.