This is one of those classic effects that I always end up not getting right. I seem to remember that there is some trouble with the whole set of "cast a spell on A so that something A touches/points to/see/hear/etc is affected". Basically the problem is that the caster doesn't see or sense that which is to be affected at the time of the casting.
To do this as an item is easy: A Muto Terram effect Touch/diameter/part to get the smooth ground and then an environmental trigger "when touching ground", and then enchant a set of shoes (or maybe a walking stick).
I still have not found a simple way of making a spell that does the same. I change back and forth between liking it (since this makes my players actually make more items) or disliking it (since many classical Mages seem to have spells to do this)
Did you think about how to make the spell the "opposite"?
Ie. something to be nasty to someone... (remembering a Hagar the horrible comic where someone says what sounds like a blessing and turn out the opposite(may the path meet you where you walk... or something like that for example(causing the poor guy to stumble and fall))
I would look at that ignem spell that burns stuff in a 7 league path. Treading the Ashen Path or something like that. You can do the same but using ReTe or MuTe instead Hermetic magic is notoriously bad at doing area of effect spells if the area of effect is not perfectly defined. And specially if you want it to be a MOVING area of effect.
Thanks for the inspiration! I have been thinking about how to do a spell to assist climbing using MutoTerram, and this spell suggestion seems to have the right format for it. Ideally the hands of the Magus would sink some inches into the cliff/wall and secure a safe grip here.
Moving in this direction might take me a step further with it, so thanks