If you are getting too many black marks from the council, get a level two
house, and make the tenants 'the punks.' After a while they should start
to complain about a hedge and will give you black marks if you do not
drastically decrease their rent. Drastically decrease  their rent, and you
will receive some white marks. Then put it up again and repeat this until
you have no black marks left. Then either replace them, agree to their
demands or make them have children. P.S. if you continue to do this, you
will receive many white marks which can be exchanged for cash. (100
marks for 10,000.)