The best long-term success for bird control (pigeon control, sparrow control, etc) will be to make changes that make it impossible for these and other birds to be able to use our structures as their roosts and nesting spots. This will cost a lot more in the beginning, but the physical devices such as bird slide, bird flite and bird netting you install will last for many years, and closing off access points with copper stuff-it can permanently exclude them from other areas of buildings. If all we do is scare them away they will return, or if not them, then other flocks that also see the structure will view it as a fine place to be.
Beyond these things there are the other options of placing wire or plastic pronged strips along ledges, wire cables running the length of ledges, the bouncing wires of the Daddi Long Legs Bird Control Wires, etc. These materials can make it physically impossible for pigeons to get onto the ledges they need, and they will go somewhere else....perhaps to another potential
Immediate relief, from a flock of pigeons or gulls for example, utilizes the role of frightening devices. Frightening devices like flickering Flash Tape, roving Scare Eyes, fake raptors, bright lights, and Bird-Gard noises will all disrupt the comfort level of pigeons, but commonly get ignored after a little while. The birds begin to realize that nothing really is happening to them from these strange devices.
If the birds are actually NESTING on the structure they are going to be pretty passionate about getting back to their nest sites, and experience shows that they may try to ignore the pain of the physical things you put in their way. Some of the best bird control folks around will tell you that you may end up having to kill a few of the birds most desperate to stay where you don't want them. If all the structure is used for is "loafing", then just making it inconvenient will be effective. Even the use of sticky materials like 4-the-Birds will be enough of a surprise to the landing bird, when the glue pulls at its feet, to cause it to look for a more comfortable place. Glues have their drawbacks though, so use them wisely.
And always remember, ultrasonic pest repellers are sold widely to chase various kinds of "vermin" away, including anything from fleas to rats to snakes to birds. A legitimate university study has yet to show that these devices are actually effective, so it would be better not to waste money on them. Placing netting, wires, strips, or other physical barriers is the best control so you don't continually fight the problem, and short term removal can be accomplished with frightening devices.