The Legacy word for "between" is "nix", and the Legacy word for "fox" is "ilit". However, Legacy words are no longer in regular use on this site or anywhere else, so I'd recommend trying to find a way to express what you mean in canon terms.

Instead of using "between" in your phrase, try using "us", the word for "before." (Click HERE for more notes on us.) Perhaps try Se dwiin het kriist us gein wo drun zu'u ahrk us nil su, "Of steel here I stand before one who made me and before empty air."

For "fox," you could say "mal sahqo raan", "small red "animal," or something like that. "Raan" would work about as well as "sivaas," I think. Look them up in the Dictionary to see the connotations and choose whichever one better suits your needs.