I have suggested this in the past, so I think it is a good law, even if the exact details need to be fleshed out and ironed out.

MK Dudi Amsalem (Likud) is proposing that a sitting Prime Minister will not be investigated for crimes he is accused of having committed.

Amsalem explains that there is an army of people trying to bring down the Prime Minister (i.e. Netanyahu) and this will put an end to that obsession.

However, because a Prime Minister who committed a crime should not just be let off the hook for his crimes, the law would include a clause saying that the period of the term of prime minister would not be included in the count for any relevant statute of limitations. Amsalem adds that in the past 20 years every single PM has been under investigation and it paralyzes the government systems. To replace a PM, the proper way is to vote him out of office in elections, not via the police.
source: Behadrei

It has been pointed out here before by commentators that a solution would need to be found for not allowing the case to go cold - sometimes an investigation can be harmed by not collecting evidence when it is still warm, and it can make it much more difficult later.

Another issue would be that certain crimes would not to be excepted form this law - such as if a PM was being accused of treason, or some other laws that put his ability to function properly into question. I would think that would include bribery, but that seems to be the basis for just about every accusation against every PM, so that would make this law moot.

Another question would be regarding re-election. When a PM finishes his term, can the open, frozen, investigation be used against him in election campaigns? Should an accused PM be allowed to run for another term with this cloud over his head? Will a frozen investigation, one with accusations that maybe he could have easily been cleared of (as PM Netanyahu has done so far of all his accusations), hurt a PM up for re-election as he has to campaign under the cloud of suspicion rather than having been able to nip it in the bud?