Paul Gustard and Andy Farrell are uncompromising and hard working - just like the defensive systems the two will employ when England attempt to make Six Nations history by winning a second successive Grand Slam in Dublin.
Farrell, the Ireland defence coach, and Gustard - who has the same role with England - are graduates of the Saracens defence school where headmaster Brendan Venter set the syllabus, and this Six Nations has been unusual as all three have been operating in the championship for the first time.
Venter is the one who has grabbed the headlines by devising various ways to make Italy at least competitive, while Farrell is reprising the role he had with England before being axed after the failed World Cup campaign of 2015.
Venter’s ‘no ruck’ strategy still grates with England coach Eddie Jones, who made a point of referring back to that most uncomfortable of matches with Italy as he savoured winning the title for a second time.
The Wolfpack explained
While Andy Farrell and Paul Gustard have used their own personalities to shape their views on defence, at heart, they still adhere to the basic principles that Brendan Venter set down. Gustard called his defensive system the “wolfpack” and even brought a wolf into Sarries training to explain the animal’s pack mentality.
A core value for both men is fast line speed – how quickly the defensive line moves to close the gap with the attacking line with pressure from the outside forcing attackers to make decisions under intense pressure. To be truly effective this line speed is allied to correct spacing between players and absolute trust in the man inside you.
Defence is mentally and physically draining and the ability to “bounce” back to your feet after making a hit must be done within three seconds to allow the defensive line to “reload.”
Communication is another key element which is why the referee’s microphone picks up an almost non-stop exchange of information from the defence as they recognise and adapt to threats.
Venter has always tried to push the envelope, taking tactics to their extremes and seeing if they work at the highest levels of the sport.
His core principals were transferred to Saracens when he arrived as director of rugby in 2009,with Farrell and Gustard schooled in the defensive system Venter insisted would best suit the club’s bid for European domination.
Schalk Brits, the Springbok hooker who has worked with all three at Sarries, said: "It is interesting that when Faz started with England he was having discussions with Brendan and Guzzy (Gustard) about defence and they helped each other out.
"Now, Faz is up against Guzzy and also his own son Owen and I don’t suppose there are going to be any conversations about defence this week!
"It is highly unusual for a club to have such an influence on international rugby defences with Brendan, Guzzy and Faz and all three of them are strong, principled people and it’s no surprise that they have got to these positions.
"They are driven individuals, with a great work ethic who really care about the guys they are working with.
"The matches will be like chess games this weekend and I think people would be shocked just how much work goes into defence these days.
"When I joined Sarries and they talked about a scoring defence I thought “what on earth are you on about?” But, it’s a fact that attack wins you matches and defence wins you trophies."
Those close to the Ireland squad believe Farrell, who will be the British and Irish Lions defence coach in New Zealand, has made them hungrier and more aggressive – values at the heart of the Saracens philosophy.
Farrell and Gustard take every try conceded personally because it signals a breach of their defence and England have let in seven during the championship while Ireland have allowed in six.