function rentBlock (address _renter, uint16 _blockId, uint _numberOfPeriods)
        internal
    {   
        
        require(maxRentPeriod >= _numberOfPeriods);
        address landlord = ownerOf(_blockId);
        require(_renter != landlord);

        
        require(isForRent(_blockId));
        
        uint totalRent = getRentPrice(_blockId).mul(_numberOfPeriods);  
        
        transferFunds(_renter, landlord, totalRent);
        createRentDeal(_blockId, _renter, now, _numberOfPeriods);
    }