The best way to attract wild boars is to use a domestic disinfectant called creolin (commonly used by farmers to disinfect animal’s homes from pigs to rabbits).
Don’t ask me how but boars instinctively know that creolin will kill all skin parasites, so they will scratch their bodies against all things that have creolin on it. You can spray the disinfectant in stones or trees (dead or alive), and boars will spread the smell to whatever they touch next (trees, mud holes, etc).
Usually boars use mud to try to kill parasites, so when they discover a tree that has creolin sprayed on it, this is what happens:
By doing that, they will also mark the territory with smells that will attract other boars. Sometimes they will mark the trees with their teeth, or remove all the tree shell exposing the naked wood.
The wind will spread the smell over valleys and mountains near by (probably for more than 1 km). True creolin has a unique smell (smells like what it is, a disinfectant) and even to humans the smell is powerful, lol (great smell, relatively speaking).
In Portugal the registered trademark is “creolina” and we prefer to use the original (don’t use other creolin-type disinfectant because it will probably smell differently). Creolin may be used pure or dissolved in water (will look somewhat milky when mixed).
IMPORTANT: creolin is an awesome attractant but if you want to keep the boars in that spot you have to put some corn near by (probably in boxes or below some heavy stones). Why? Because boars don’t need to scratch their fleas everyday, but they will eat every single day (and night). Attract them by their nose, but keep them there by their stomach.