[font=Arial]My personal opinion is the same as many mentioned:
[color=#FFFF99]This will cause traders to avoid Rheinland... just for the fact that they can get taxed for being there.
Just imagine how a trader must feel to possibly get taxed again after having managed to get to Rheinland in one piece through the pirates elsewhere or having survived a pirate encounter inside Rheinland:
"Why in blazes should I get taxed again if they didn't protect me in the first place?"
If at all, you should make is as Jinx suggested an 'escort fee' and protect the ship until it reaches a border. Simply having 'yet another tax' with nothing in return won't do.