Is there another wall encompassing the entire of Paradis for Marley to use?
Yes, there is an outermost wall in Paradi Island other than Maria, Rose, and Sina. So far it's not known whether it surrounds the entire island or just a portion of it, and its purpose is not clear.

Speculation: It could be a staging area for the titan transformations, but more importantly a barrier to prevent them from crossing the ocean.

On the inside covers of the tankōbon volumes are written codes in inverted Katakana, and one of them gives a clue to the walls' origins:


   In the new world, great walls had previously been prepared.


Sources:


(Japanese) http://shingeki-kyojin.com/archives/26439768.html
http://calorescence.tumblr.com/post/51450703198/did-you-know-the-inside-covers-of-the-japanese