Brennan Cox during the 2022 AFL Round 19 match between Richmond and Fremantle (Photo by Cameron Grimes / Zero Digital Media)

Fremantle has locked away a key pillar of its defensive unit, signing key stopper Brennan Cox on a mega six-year deal.

Cox was already contracted to the Cockburn club until the cessation of the 2024 season, however, after recomitting under Justin Longmuir, the 25-year-old will now remain in purple and white until the end of 2030.

The defender's new deal comes off the back of back-to-back top-10 finishes in Doig Medal counts, with 2023 also acting as the season Cox surpassed the 100-game mark.

Alongside the ilk of Luke Ryan, Hayden Young and skipper Alex Pearce, Cox acts as the face of the Dockers' rearguard - a unit that has been selective built, off-season after off-season.

Locked away for seven years, Cox's agreeement eclispses the deal signed by Young last season, one in which the man-bunned interceptor tied his future to the Dockers until the end of 2027.

Cox's contract now sees him hold the most job secruity within Fremantle's four walls, with the South Australian edging Luke Jackson and Jye Amiss - both of whom have signed on until 2029 - as well Caleb Serong and Luke Ryan, each inked until 2027.

“I really enjoy being here and I'm really driven to be part of that group that brings the first premiership to Fremantle,” Cox told Dockers Media.

“I love the boys here and I've built a really good connection, lifestyle and home here, so it was an easy decision in the end.”

The Woodville-West Torrens product also wished to pay praise to those that work around him inside defensive 50.

“All over the team we're pretty young and a lot of the boys have signed on, so it's going to be the same group for a fair while and I'm excited to see the growth in the younger boys,” Cox said.

“I obviously have those connections with the likes of Luke (Ryan) and ‘Moose' (Alex Pearce) and over the past few years I feel like we've really built something as a back six and I feel like we can really grow and take it to another level next year.”

Cox began life with Fremantle in 2016 after being drawn across the border with the 41st pick of the draft.