"Shackle the body, and the anguish lasts only until death. Shackle the soul, and the wicked can be punished for eternity."
—Inquisitor Laerin

Soul Snare

{W}, Sacrifice this enchantment: Exile target creature that's attacking you or a planeswalker you control.

"Body and spirit are sworn enemies. They will take any excuse to be rid of each other."
—Tariel, Reckoner of Souls

Murders at Karlov Manor Commander

{W}, Sacrifice Soul Snare: Exile target creature that's attacking you or a planeswalker you control.

Starter Commander Decks

Modern Horizons 2

"Shackled the body, and the anguish lasts only until death. Shackle the soul, and the wicked can be punished for eternity."
—Inquisitor Laerin

Commander 2021

If Soul Snare's ability targets a creature that's attacking a planeswalker you control, but that planeswalker is no longer on the battlefield as the ability tries to resolve, the attacking creature will be an illegal target and Soul Snare's ability won't exile that creature.

Sacrificing Soul Snare is part of the cost to activate the ability. Once you activate the ability, no player can do anything to Soul Snare to stop you from activating it.