Ms Clark has had to deal with allegations that her husband,Peter Davis,is gay,ahead of the publication of Investigate magazine.
Ms Clark says her husband is not gay. She has accused her opponents of trying to attack her husband with baseless,"school-boy smutty rumours".
Ms Clark said the rumours had been"assiduously spread"by her political opponents and were part of a"poisonous"campaign against Labour by right-wing activists and fringe groups such as the Exclusive Brethren.
Asked what proof she had to back her claim,Ms Clark said people had passed information to her.
A"serious media source"had been following a story that the Exclusive Brethren had hired a private detective to follow herself and her husband.
A separate"very credible source"had said a private investigator was approached to do the job and had turned it down.
"I start to put two and two together,"she said on Newstalk ZB.
Ms Clark said she was unsure whether she or Mr Davis had been followed.
"I don't know because the work of such people ... is not to be seen when they do it,but certainly my husband and I have been taking extreme precautions about how we move around for some time."
The Wellington Dominion Post reported the Exclusive Brethren had denied hiring detectives to follow Ms Clark or her husband around.
The secretive sect appear to have dedicated themselves to unseating Labour.
They waged a campaign worth more than $500,000 attacking Labour leading into last year's election,and correspondence with the Chief Electoral Officer,released under the Official Information Act,showed they wanted to spend $1.2 million in support of National.
They were told,however,that spending of that magnitude would be counted in National's spending.
Since the election,Exclusive Brethren members have been frequent visitors to Parliament,watching from the public gallery on most sitting days.