It's not technically against the rules, but I am not a big fan of targeted mana abilties in general.
Secret Soil comes into play tapped.

, Pay one life: Add

to your mana pool.
Whenever Secret Soil is tapped for mana, target creature you control gains protection from the color of your choice until end of turn.
Now, it uses the stack again, but it still gets around split second.
Wouldn't the triggered ability wait until the split second card was off the stack before going on?
502.58a
Split second is a static ability that functions only while the spell with split second is on the stack. "Split second" means "As long as this spell is on the stack, players can’t play other spells or abilities that aren’t mana abilities."
I agree that it needs the until eot clause.