Look, porn is everywhere. He's a big boy and if he wants to watch porn, it's not really fair to stop him. He obviously still watches porn, the signs are everywhere (keeping the old stash, saving some of the photos on his phone, reading the maxim magazine in the bathroom) he just looks at porn when you're not around. My boyfriend watches porn and I used to hate it/find it dirty but you have to realize that it's harmless, these girls are doing it because they want to and they like it, and that stopping him is only going to make him resent you.
Rather than worrying about him watching porn, you should focus on being more sexually intimate with him. Guys either watch porn because they're not getting enough or because they have fantasies they're embarassed about/you won't fulfill. I notice a pattern; when I work a lot or I'm on my time of the month, he watches porn, but all other times he never touches it. To stop him from watching it, give him what that primal part of his brain needs. If you won't have sex with him, he's gonna watch porn.
And to answer your question, yes. He will probably watch porn. But I doubt he'd do it at work. Guys usually don't watch porn somewhere they can't ... relieve themself, if you know what i mean.
Don't try to stop him from watching porn if that's what he likes, it will only frustrate him and guys really don't like being controlled. How would you like it if he made you completely cover up your body because he found it disrespectful for you to show your skin to others? It's your (and his) life, live and let live.