How to prevent other people using the specific IP address?

Solution 1:

If you mean DHCP, then there are 2 possibilities:

1. Reserve your MAC in the DHCP list, but as you say, it does not seem to work, therefore it is a bug.
2. Ensure the DHCP pool is less than the subnet width, then apply a static IP address to you PC which is outwith that range. ie, for 192.168.0.0/24, set a range of 192.168.0.20 - 192.168.0.50, then configure 192.168.0.70 on your PC.

However, ultimately, there isn't anything you can do to ensure it will not happen since people can apply whatever IP address they want if they have permission. All you can do is reduce the possibility.