In the “Example Contract of the German Renter’s Association”, interests of tenants and landlords are considered equal. Have the rental contract reviewed prior to signing by the rental office or other authorized authorities, saving you plenty of annoyance.
You should insist that your landlord offer’s you the customary bank interest rate for your security deposit. After all, throughout the years it is still your money that was provided as a security. In accordance with the law, the security deposit can’t be more than three months’ rent.