The "boulie tacker" could be using a car or motorbike to drop tacks on Yarra Boulevard, say police who have announced a $50,000 reward and plans for infra-red CCTV cameras in a push to nail the mysterious saboteur.

"We think that the person dropping the tacks is mobile in a car or on a motorbike," Assistant Commissioner Glenn Weir said on Wednesday.

One of the mobile CCTV units set up to keep watch on Yarra Boulevard. Credit:Eddie Jim

"It’s really hard to detect those people. So we need to look at different ways to catch the people responsible."

The unknown offender has been intermittently active since 2014 and is believed to be behind about 1000 punctured bike tyres along the Kew boulevard, with some cyclists left seriously injured.