Long time lurker, first time poster.
So if I have my employees sigh a paper stating that they will rob banks for me, does that make it legal? I think you see where I am going with this. Two parties cannot enter into a binding contract (work agreement) in which at least one of the parties knows that the agreement may violate the law.
As a small business owner, the one thing you do not want to mess with is labor law. They’ll be on you faster than white on rice.
Anyway more to come about me later. But for now, just know that my name derives from the fact that we have created our “secret recipe” BBQ sauce and use it for our BBQ pies, but we also sell items like pulled pork and beef sandwiches and ribs. I have been open for four months, having taken over an established business and changing nothing except the BBQ aspects.
We set monthly goals and have an incentive programs, for instance we do trades with car wash, movies, other restaurants and others, we bundle the package for our 2 managers if we can reach the goals, they get the package if not then we 3 sit down and go over what went wrong. I focus on things that are directly in there control. food costs, customer service!
Rockstar gets my vote 
Each employee is different, and rather look at employee incentives as punishment or a way to potentially pour money down the drain, get creative.
I think most importantly, employees need to understand your business, how it makes money, what profit looks like, and how it benefits them when you achieve it. Some employees will interpret it as a bonus, some as a scorecare, and the rare few… see it as an opportunity to be educated on business matters and be allowed to voice their ideas to consider.
Who knows, you might just accidentally train a future manager for your next expansion site
My 2 cents.
Jay