Sorry for double post, can’t edit on mobile. You can also try

/ac “Heart of Stone” <tt>

This will use it on the target of your target so if you’re tanking it will use it on you and if someone else is tanking it will use it on them, it won’t work if you don’t have a target however. You can also focus (default shift+f) on a target you want and replace the tt with ft in the macro to use it on your focus target.