Okay, but unless your program is going to run for the life of the dog, and the combined lives of all the dog 'registered', you are going to have store that unique id somewhere between runs of this program. And accessible to other programs that might need to deal with it. And that means that on subsequent runs you are going to have to read it back from some persistent storage and then set it.

Unless you can set it (at least once) it never has a value. And the only way to set it without using a setter, is to initialise it using a constant. Are you going to hard code all your unique ids into (all) your program(s)?