Treated lumber vs. not treated

I have plans to put in a new wood fence, and have to decide on treated vs. untreated lumber. My environmental side says go with untreated. But will it rot away in 10 yrs? Or does that not matter, wood is supposed to rot away. Untreated would be cheaper. I should research what the compounds do to dogs and wildlife.

From Home Depot: The most common types of chemical used to treat wood are Alkaline Copper Quaternary (ACQ), Copper Azole (CA), and, the newest type, Micronized Copper Quaternary (MCQ). Pressure treated lumber can last 20 years or more, and most pressure treated wood comes with a limited lifetime warranty.