[Ron, I had one for a year or so also and your question made me curious. In an article written by Nathan Cope in August 1997, titled, "Shrimp for the Tropical Marine Aquarium". He states that in the species Lysmata amboinensis and L. grabhami (Scarlet Cleaner or Redline shrimp), of which the skunk cleaner is another common name, "Lifespans of 6 or more years are not unheard of!".
I was actually very surprised by that, I thought two years would have been a long time.]