"It was a good time to do something together," Mr Casson said.
"I am so proud of him as he fought long and hard to get into the army. He had a couple of injuries to his leg that he had to get fixed up but he persevered."
He said that while he is always concerned for his son's safety, he was not going to wrap him up in cotton wool.
"It is his choice to serve. My mum and dad had concerns for me when I was deployed overseas, but I would never stop my son from doing what he wants to do."
"He (Jon) had watched me serve as a police officer and he wanted to do the same sort of thing." Mr Casson's protection office role took him to various diplomats posts around the world to peacekeeping roles in a range of locations, including Papua New Guinea, Tonga, Solomon Islands and East Timor.
He is also a trained diplomatic protection officer and has protected several New Zealand Prime Ministers and the likes of the Sultan of Brunei, Rod Stewart, Rachel Hunter and Nelson Mandela.
In 2008 when he was 42, he was on duty in East Timor during the attempted assassination on then president of East Timor Jose Ramos-Horta.
"I did close protection over there with various diplomats including Ramos-Horta. I was there during the assassination attempt of him in February 2008."
"It's quite a vivid memory because of the high tension there at the time."
As a protection officer for local New Zealand politicians, Casson said one of the biggest challenges is staying alert at all times.
"You are armed, and you need to remain alert for these long period of times."
"In New Zealand it can be boredom, but when you get into these situations like in East Timor where they have had failed assassinations, it is very different."
"It is a matter of changing your routine for the area you are in and making sure your diplomats are safe from the rebels there."
Mr Casson said that in diplomat training you are trained to take the bullet for the diplomat and you try your best to protect them.
"You have taken an oath to protect life and property and you have to take that seriously."
He has taken the lessons of his life in the police force over into the council chamber.
"It is always just about being alert of what is going on in the community. After seeing that side of life it gives you a different perspective."