What about getters and setters?

// implicit logic in the setter
//
public class Account1
{
    // typical account details omitted ...

    private decimal _balance;

    public decimal Balance
    {
        get { return _balance; }
        set
        {
            // both logic for adding and withdrawing cash would
            // end up here
        }
    }
}

// explicit methods with their own rules
//
public class Account2
{
    // typical account details omitted ...

    public void Add(decimal amount)
    {
        // adding rules go here
    }

    public void Withdraw(decimal amount)
    {
        // withdrawal rules go here
    }

    public decimal Balance { get; private set; }
}