I pretty much did the same thing with the clear plastic, My octo has never tried to escape, there are many of other ways for him to thats how i know he hasnt. The astro turf method is ok they dont like the feeling of it its too "sharp" for them because they have so much surface area. There is no "escape proof" tank really, and everytime you get and octo you take a chance. You just have to figure out what works best for you. Another Idea a fellow friend did, was to take a piece of plexiglass and put it on hinges he glued it down except for int he back where he could lift the maybe 3" deep but all the way across the back piece up on that he had super glued a lock onto the back of his tank and onto the top of the plexi glass he drilled TONS of VERY fine holes into the plexigalss.. and his pump was submersible and octos dont really like alot of water flow but they do like CLEAN water!!! and HIGH SALINITY!
So maybe you could try that if you dont mind glueing it to your tank???????
Personally I wouldnt but Hey if you really like octos and if that one goes (since they have such short life spans, it will) and you get another you will have the tank ready.