“Salty Dog” is nautical slang for an experienced sailor who has spent much of their life aboard a ship at sea. A salty dog is often given increased credibility by ship mates in matters pertaining to ship-board life and duties. Also known as an “old salt.” http://en.wiktionary.org/wiki/salty_dog
"Salty dog" also means ornery, as in the T-Bone Walker

T-Bone Walker

Aaron Thibeaux "T-Bone" Walker was a critically acclaimed American blues guitarist, singer, songwriter and multi-instrumentalist, who was one of the most influential pioneers and innovators of the jump blues and electric blues sound. He is the first musician recorded playing blues with the...

 tune "Ain't Salty No More." In US folklore and song, salty dog has an older sexual meaning. For example, in the traditional song "Salty Dog Blues"

Salty Dog (song)

"Salty Dog Blues" is an early 1900s folk song. It is in the public domain. It has been recorded by blues, jazz, country music, bluegrass groups and other styles. The oldest recordings of the song credit Papa Charlie Jackson, who adapted the song directly from the African-American traditional for...

, the lyric "Honey, let me be your salty dog" translates to "Let me be your sexual partner."