"Rob is a strong ball carrier and a good tackler. I'm going to have to make sure I commit when we're on defence."
He agreed the Magpies' defence required vast improvement after the leaking of five tries against North Harbour last weekend when 32 tackles, three of them his, were missed.
"We can't do that against top teams like Canterbury. We'll have to put in an 80-minute effort," Horrell said.
His combination with Highlander Richard Buckman in the midfield has been one of the keys to the Magpies' success to date this season. Their solid defensive work has been matched by their ability to break the defensive line with a variety of options.
"Bucky has come off a successful Super season and is playing well. Hopefully our partnership continues for a while to come," Horrell said.
He pointed out the success the Magpies are experiencing this year has a lot to do with the work put in during the last three seasons with the same coaching staff and a core group of "really good players".
"We haven't finished with a title and it would be nice to do that this season. It would also be great to keep the shield for another year too," Horrell said.
Magpies head coach Craig Philpott will announce his travelling squad later today.
The former Cantab obviously wants to keep those in charge of the team he played for a couple of decades ago guessing as long as possible.
Philpott agreed the Canterbury outfit thrive on structure both defensively and on attack.
"It's important we make those structures uncomfortable."
Hawke's Bay age-group product and former All Black lock Dominic Bird will start for the hosts while former Magpies hooker Ged Robinson is expected to get game time off the pine.
All Blacks prop Nepo Laulala will make his first ITM Cup appearance of the season and another prop with recent All Black experience, Joe Moody, will start at loosehead.