New Delhi, Feb 2 : Pitted against farmers who earlier used the sheer power of their tractors to break through barricades and other obstacles in their march towards Delhi, police has now come up with innovative methods to check their advance -- iron spikes and wooden boards with big nails cemented on to the roads. Also, the iron barricades have been further fortified by concertina wires, double layers of concrete slabs further strengthened by pouring in concrete mix between them to make them difficult to move even by tractors once the concrete solidifies. Earlier, police had dug up trenches across the roads and even parked buses and other heavy vehicles to prevent the farmers from moving towards Singhu, Tikri and other borders, but could not succeed. The protest sites on the Delhi borders now are marked by heavy presence of police and paramilitary forces in riot gear, apart from buses parked across roads to dissuade more farmers from Punjab, Haryana and western UP from joining forces at the protest sites at Singhu, Tikri and Ghazipur. "These iron spikes and nails are tyre-killers used to prevent the entry of tractors into Delhi. We are using these in the backdrop of what happened on January 26 and the violence that followed," a senior Delhi Police officer said. Even drones are coming in handy to keep a vary eye on trouble-makers, with police doing intensive checking of vehicles on the Delhi border that has resulted in massive traffic snarls at the entry points to the national capital. /IANS