Yes. Deer liver, heart,the fat from inside deer with a bit of beaver oil sack all ground together.
Beaver meat is hard to beat as well, it is good to grind it also. Seems like they need to get every bit of it when they work it.
Back in the days when I trapped foxes, many moons ago, I had a period of luck using slightly tainted beaver meat. Of course I had access to beaver carcasses at the time.
For the most part I used lure and a few drops of urine.
I also had success pouring approximately one ounce of fox or bobcat urine right down the hole and using nothing else.
Frankly, I do believe all you need is something that stinks.
Sometimes I think the types of lure lures used and/or whether to use fresh or not so fresh urine is overplayed. If it stinks, just drop it down the bait hole and call it a day.
Years ago there was a local land manager for the Game Commission who was an accomplished fox trapper. He handled mostly complaints and foxes were frequently his target. As a Commission employee he was not eligible for bounty claims.
Before I get carried away on that tangent, let me say the gentleman has his own ideas about trapping and he was quite successful. He used just lure, no special brand but usually one compounded by a Pennsylvania lure maker. I am talking here about Danko, Lippert and Hawbakers. There were probably some others too but I can't recall the names.
Getting back to the bait, I'd say 6 of one, a half dozen of the other.