There's no way you can do that. If you don't want to get rid of graffiti on your property, you don't have to.
Not according to the city's policy. :/
http://www.toronto.ca/graffiti/qanda.htm
What do I do if I see graffiti vandalism on my property?
If you find graffiti on your property, it is your responsibility to clean it up. You can either do it yourself or you can hire someone to do it for you.