decorator pattern decorator limit

I am currently writing a program using the decorator pattern. I am trying to find out how to limit the amount of decorators I can add to the first class. Such as:

Pizza plainPizza = new PlainPizza; Pizza sausage = new Sausage(plainPizza);

How could I code this where I can be limited to the amount of decorators I add on. Such as if I try to add this on top of the previous code:

Pizza pepperoni = new Pepperoni(sausage);

How can I prevent it from allowing pepperoni to be added/wrapped?

Thank you!