Bird Repellents come in two formats, liquid and gel. Liquids are sprayed on to a surface using a garder pump sprayer and create a tacky, "wet-tar" like surface, on which the birds don't like landing. Gels are applied using a cartridge gun, in parallel beads, which skin but never set, presenting a jelly-like, unstable surface on which birds don't like to land.
Use bird repellent liquid on large surface areas. Use bird repellent gel on linear areas.