Saints have conceded in 15 of their 16 Premier League outings this term and slipped to the foot of the division ahead of Saturday’s trip to Fulham.
The Welshman accepts tightening up one of the top-flight’s most porous defences is among his greatest challenges.
“We have to pick a side that can hopefully defend better,” he said, looking forward to the visit to Craven Cottage.
“Having kept one clean sheet in 16, that’s not good enough. If you’d kept three or four in 16 games then you’re sitting in a different position now.
“Yes, there would still be work to do but we’d be in a better position and that’s what we have to do.
“We can’t dwell on anything. We know we’ve had defensive deficiencies. And that’s not just individuals, that’s as a team and as a collective.
“We need to be better and that’s why we’re here. With the greatest of respect, if there weren’t deficiencies then we wouldn’t be here.
“Clubs only recruit a new manager for two reasons: either they’re doing fantastically well and someone gets poached or they’re not doing well and someone loses their job, and we’re in the latter.”
Only 14th-placed Bournemouth (34) and second-bottom Nottingham Forest (33) have conceded more than the 30 goals let in by Southampton.
Saints were uninspiring against Brighton on Boxing Day, with major mistakes from goalkeeper Gavin Bazunu and left-back Romain Perraud helping gift the visitors an insurmountable lead.
“Problems are never solved overnight, unless they are minor ones,” said Jones.
“It’s just work and people buying-in to everything.
“There’s a decent group that want to learn but we have to identify the problems, show them where we can be better and then be better.”
Jones backed Bazunu following the defeat to the Seagulls, describing him as “fantastic keeper”.
The Republic of Ireland international, who was also at fault for an opposition goal when Southampton stumbled past Sky Bet League One Lincoln in the Carabao Cup last week, could retain his starting spot as Alex McCarthy missed the Brighton game with an ankle issue.
Jones expects a stern test from Fulham, who sit ninth following promotion, and is wary of their 10-goal top scorer Aleksandar Mitrovic.
“They’ve a lot of players who have been there regularly and been there years, so they’ve got a lot of continuity,” he said of Marco Silva’s Cottagers.
“They have a goal-scorer that scores whatever league he plays in, internationals, and it will be a tough game. It always is.”