Pebble ballast is commonly used on modern flat roofs, gulls have taken a liking to the pebbles and have developed the strange behaviour of picking them up in their beaks and dropping them from height onto the ground below. This is a serious hazard and to prevent this from happening 19mm net is installed directly onto the pebbles to cover them completely. The netting is installed in the same way as we would a normal bird net.  The gulls are unable to get to the pebbles and the hazard is obverted.

The net is strong enough to still be walked on over the pebbles.