To remedy 'ordinary' pigeon problems in southern Ontario cities, those who don't like the look of netting off the perches sometimes rig a fine wire pulled taut 1" or 2" directly above and parallel to the main perches. If it's a wide perch such as a 2x4 laid flat to top off fence posts, you may find you need to run 2 wires, 1 above each edge.

Most birds, including pigeons, aren't able to use the wire for roosting and there won't be space for the birds between the perch and the wire. The birds soon rework their roosting routine in favour of more comfortable options. If you're lucky, they'll choose new perches on & over your neighbour's outdoor space. Anyway as long as they aren't on/over yours any more... The main risks to this method are (1) instead of moving away, the pigeons do find new perches that still soil *your* space; (2) your swing set frame, fences, roosting branches overhanging your yard etc etc may become unattractive, depending on how the rigging is done; (3) it ruins the perches for nearly all birds.

This method is of limited use when kids also use the swing set frame as monkey bars.

Assuming this problem will recur every year and that maintaining such rigging will be no fun, I would research how to create an alternative roosting pattern by judicious planting of suitable trees or shrubs. How this species of pigeons feeds and flees will determine what species and distances to try. Local flock characteristics may not match precisely the available research so you may need to try more than once.

It's never easy to blend human requirements seamlessly into nature's way, but don't give up. As for legality, those solutions are legal in my city, though in a condo situation it would require the co-operation of the board to plant on shared property; your local pest control companies may be able to point you to the appropriate government departments governing such things.

Best of luck!