There isn't actually a 'Secret Service' for leaders of Tir Tairngir. As a whole, such roles would be taken by the members of the Peace Forces (either the police or military branches). High ranking members, such as the Council of Princes may get Ghosts as part of their detail, but they also have Paladins. Paladins aren't exactly bodyguards, but are more like a cadre or disciples. They often are sworn to serve and protect the person they follow, and they take those things very seriously. The thing to remember about Paladins is that they serve the individual, not the office.
And then you have hired bodyguards and the like, as well. Oh, and don't forget the Information Secretariat keeping an eye on things to try and prevent trouble from breaking out.