Only way to restrict or control slums is NOT TO ALLOW SLUM RESIDENTS TO VOTE in any elections from local municipal elections to general elections.
These people are seen as vote banks by political parties and local party workers support these people, they provide them land, water, electricity and other necessary things to get their votes in return.
If we deny them their voting rights, no political party worker will help them and they could not live there without basic necessities like water, electricity etc.