What does "tie me kangaroo down, sport" mean?

"I was trying to come up with new songs that had a simple chorus that everybody in the club could join in with. I liked (Harry Belafonte's) 'Hold 'Em Joe.' There was a line that went, 'Don't tie me donkey down there, let him bray, let him bray.' And I thought, 'That's good. I can change that and make it an Australian calypso. Instead of a donkey, I'll have a kangaroo in there somewhere.' "Eventually, I came up with 'Tie me kangaroo down, sport.'