Question about categories in Opencart 1.5.5.1

Question for those who really understand how categories work.

Let's say I have a cat design called "mycat" in all 3 categories - cats, animal, and home

I want this design to have URL www.mystore.com/cats/mycat

This works fine when "cat'" category appears first in the category list. But many times "animal" appears first in the category and this results in www.mystore.com/animal/mycat

I know in 2.0 version I can select main category. How can I make sure that my main category is always "cat" with this URL www.mystore.com/cats/mycat

When someone is in animal category they can still find the design but the URL is still www.mystore.com/cats/mycat

Please help

thanks
D