You might be underthinking it. As a trial attorney, there are always a few things that the opposing counsel will go after if they apply to my witness:
1) Is witness being paid by the defense?
2) Does the witness have a prior crime of moral turpitude on their record?
3) Has the witness been caught lying on the stand?
Of all 3, the last one is by far the worst. And usually that takes the form of showing, via circumstantial evidence, that something the witness said is untrue. Rarely, if ever, have I seen a witness take the stand with an actual conviction for perjury on their record.
If you were a juror, why would you trust a single word that comes out of the mouth of someone who will have to admit that on a prior occasion, after taking an oath (exactly like the oath he just took in front of you), he intentionally lied on the stand? In fact, as a juror, you will be instructed by the judge that due to the witness's prior lies, you are free to disregard every single word that comes out of the their mouth.