The reason why citrus works is because it is acidic, and cider vinegar works well too.
Another thing that works well is kerosene, and sand...then wash with lava soap to get the kerosene smell off.
If you find some good fish cleaning gloves, they protect from the smell, and the hand, if you are lousy with the knife...and that is nice to know if you slip.
For the ultimate hand cleaner that works on everything from paint tar, to axle grease and more...I have found that Stockhausen, Inc. out of Greensboro North Carolina (1-800-334-0242) makes something called Cupran Special
It can be ordered on-line, by googling it. Buy a case of this and I can tell you that you can forget about the rest of the hand cleaners you own...it is that good. Not very expensive if you split a case with a friend or family member and it lasts a long time since you don't need much for it to do the job.