While I agree with any premise that will get you to connect to the now and practice mindfulness but I think you need to put a disclaimer somewhere and ask people to 

PLEASE do not do this stacking in any National Park anywhere in the world. 

It disturbs the natural balance and homes of little critters. It also takes away from the 'naturalness' of the area. 

And if you do practice this is a public space, remove the rocks when you're done, just as is suggested. 

@cloudcore 

Sending love and thoughtfulness. And happy mindfulness