4 Dec, 10:19
Grand Slam winners Fiona Coghlan and Nora Stapelton have returned the Women's RBS 6 Nations trophy to Chief Executive John Feehan at the Six Nations offices in Dublin.
Marcus also talked about the sacrifices he has made to get to where he is in sport today - and of course how it felt to be a part of the Grand Slam-winning Ireland squad!
Marcus spoke about how he had seen many players who had all the talent they needed to make it at the highest levels of the game, but how staying focused and sticking at it is more important than talent or ability in the end.
He stressed the importance of setting goals for yourself as an individual and as a member of your team.
The visit to St. Nessan's was part of a Garda campaign called 'How Big Do You Feel?'
The campaign has two goals, it teaches young people about the dangers of knife crime and it inspires them to follow in the footsteps of their heroes and dream big.
Some people think knives can protect you, but that isn't true. You can learn more about the 'How Big Do You Feel?' campaign here.