When confronted with a difficult passage that just isn’t getting any better, most of us will isolate the left hand to improve our accuracy. We may change from arco to pizzicato to isolate the left hand. We may “shadow bow” the passage. Perhaps we may finger the strings in the left hand alone, completely taking the right hand out of the equation. All of this is valuable, and may indeed help solidify the section in question. I would submit, however, that it is equally important to isolate the right hand as well.
It sometimes happens that, when we are having a problem with a particular excerpt, what we think is a left hand problem is actually a right hand problem. Especially if repeated practice and focus on the left hand does not fix the issue, this may indeed be the case. Whether this is true for a particular passage or not, focusing on the right hand will only solidify the technical requirements for that passage.
What I suggest is playing the passage in question exactly as you would in the right hand, but using open strings. For example:
Such a practice method works whether we are plucking or bowing. When plucking, we should be specific as to which fingers we are using in the right hand. Too often students are lax in this area, and this can be the source of a number of hidden clarity issues.
When the right hand is isolated for pizzicato playing, it might look something like this:
If you actually try this you may find, as I do, that this is actually quite awkward for the r.h. This may lead you to change the r.h. fingerings to something like this:
This is a much easier r.h. fingering for most players. Such changes in r.h. fingering can become clearer through r.h. isolation of difficult, or sloppy, passages. I suggest isolating the right hand/bow as well as the left hand for true instrumental mastery of a passage.