The victory gave the South Africans an unassailable 2-0 lead in the four-match rubber.
The home side won the first Test by 189 runs in Johannesburg two weeks ago. The third test starts in Cape Town on Friday.
The West Indies suffered the first whitewash in their history when they were beaten 5-0 in South Africa in 1998, but Lara felt there would be no similar humiliation.
"A whitewash is a possibility, but I'm ruling that out," he said. "It's not going to happen."
The captain added: "Our fielding and our bowling definitely have to improve and our batting has to be more consistent.
"They are things we have to work on, but we're not going to get too depressed about it because I'm sure it won't happen again."
Lara's South African counterpart, Graeme Smith, was not taking anything for granted.
"We've got to work hard, put a knife to our throat because it's so easy to lose focus," he said.
Paceman Makhaya Ntini took three for 72 in the second innings to end the year with 59 wickets and become the leading test wicket-taker in the world in 2003.
"It's terrific, we're all so proud of him," Smith said. "As a fast bowler you have to perform in different conditions around the world and he's done that.
"He's grown so much as a person and as a bowler. He's realised he's got to work hard and he's adapted his bowling to get closer to the stumps. He deserves his success."
