However, his first season ended in disappointment as Tarxien Rainbows finished in 10th position in the Maltese Premier League, requiring the club to be relegated to the First Division.

Mamo went into the 1998–99 season, hoping to help Tarxien Rainbows gain a quick return to the Maltese Premier League.

The move was an instant success as Mamo helped his new club finish in 1st position and win the Maltese Premier League title.

The 2002–03 season was one of triumph for Carlo, as he won his second Premier League title, and his first with the Sliema Wanderers, making 17 appearances and scoring one goal.

reached the heights of Maltese football during the 2006-07 season, as Mamo captained his team to the title for the first time in the club's history.

Carlo proved instrumental in the club's success, forming a solid partnership in the centre of the defence with fellow Maltese International defender Luke Dimech.

However, the club suffered the loss of many important players and finished in 2nd place in the League with Carlo making 19 appearances and scoring one goal.