And a spokesperson told the Daily Mail he had the tattoo changed to the dog when a touchup appointment went wrong:

“Mr. Stallone intended to refresh the tattoo image of his wife Jennifer, however the results were unsatisfactory and, unfortunately, unfixable. As a result, he had to cover the original image with a tattoo of his dog from Rocky, Butkus.”

Source: https://www.buzzfeed.com/mjs538/sylvester-stallone-tattoo-replacement