(1) Offer rehabilitation (many homeless don't willingly take advantage of this).
(2) Regularly push them out of where they are staying with officers. If necessary, use hoses or w.e.
People will either leave because they can't stay there or they attempt to rehabilitate. This is what they do most places outside of California.
This method often leads to rehabilitation, because they don't really have a choice. Those who don't want to be rehabilitate leave and start a life the next town over, live in the woods, what have you.
It's better for everyone in a society to hold each other accountable -- be apart of the society or leave. Many homeless are drug addicts and / or mentally ill, they need help, but you can't help them (unless they want to). By holding everyone accountable, everyone will be better off.