Algodoo

box wave

why box wave ?

because you have hidden boxes under ground

ohh

nice but you can also just script something like this in on colide thing:

(e)=>{e.this.density = +inf; e.this.attraction = -10000}

or something and then add script for limeted time push away to awoid making a anti stuff zone =P

here is a example http://www.algodoo.com/algobox/details.php?id=47039