The Singapore model is also to be a 750km^2 microstate island. American laws around drugs have always been punitive and you could fit Singapore inside your average county.
Absence of land borders simplifies the problem considerably.
There is a land border with Malaysia.
How many km?
And heavily punish the users (which is the only way to actually win a war on drugs)
The evidence doesn't seem to bear this out. Texas has punitive laws around drug use and also plenty of drug users.