Foam marker for sprayers and planters or drills

So I posted this elsewhere.....and I wonder if anyone has done one of these.   It would seem to me that an enterprising guy could make and sell these markers to folks like us.   Not many DIY'rs anymore and just buying a commercial version of this that works would be worth the price of admission.   Good project for a home based small biz.  Market via the web for free.   The world would beat a pat to your door?   grin. 

In todays times a radio transmitted "trigger" could be a Big Bang for the buck......and would allow to mount virtually anywhere quickly / easily.   USPAT BR549.

eprints.nwisrl.ars.usda.gov/id/eprint/420/1/530.pdf