DespairingOfMankind

• A sign that says 'Asda trolleys will be immobilised if taken beyond the red line
  
• A very visible and obvious red line
  
• Sufficient abandoned trolleys at a distance <=x beyond the line (where x is the distance one can push a trolley while the immobiliser comes into play - Mike has watched this drama enacted on one occaision) to almost completely block the path.
  

Bobacus has indulged in the aforementioned testing of TrolleyImmobilisers at Tesco. I'm convinced that they work :)