Will Everyone Hate This Baby Name?
In the United States today, Fox would be a bold choice. It would come across as a bit uncommon, as you prefer, but also as appealing to many with its confident sound and origin in a nature word. Short, brisk word names are on the rise, and Fox fits right in with them.
As you note, though, the word's meaning is very different in your country and among your family and friends. If you honestly think the name will play badly to your community, that's not a good sign. It's one thing to push people out of their comfort zone. Every generation does this, which is why I get so many questions involving grandparents not liking a prospective baby name (I advise that grandparents need to butt out). And convincing your nearest and dearest to warm to a name is certainly possible.
But this is more about how your son will be perceived for life. Would everyone meeting him or seeing his name for the first time have an uncomfortable association with a nuisance animal? (Americans, think about how you'd feel about a child named "Rat.") That's a red flag, and an indication that you and your husband should probably shelve this name and move on.
In fact, shelve Lex too, since your husband hates it, and start over with the goal of choosing a name you both like. Fox and Lex share so many characteristics that I'll bet you can find a new name you’ll both be happy with. Maybe one of the Fox-y names on this list would work, or an unusual ends-in-X pick such as Dax, Dex, Pax, or Rex. And of course, you can venture beyond X-endings for many more uncommon choices—one of which is bound to be the right pick for your new little one.