To answer your main question aout no law prohibiting alleged slander in political ads, there is one. It's the same one that ordinary citizens can (and do) use when they feel they have been slandered by some public statement by another individual. Problem is, what constitutes slander is a very subjective determination. But anyone can have their day in court by suing and having a jury decide, That said, court rulings have well established that public figures by their very position have to expect that things will be said about them that may not be wholly true, and there is a much more stringent test for them as to what constitutes slander.
With respect to your stated horror at the law in Alaska for hunting wolves, you should be aware that the wolf populations in many areas of the state have increased to the point where they are a substantial threat to other wildlife, namely moose and caribu. They therefore have been declared predators and bounty hunting is permitted in order to bring the population under control. If you would do a just little research you'd find that Alaska (and Gov. Palin) are not unique in this respect, and a similar situation exists in a number of other states which permit bounty hunting of wolves and/or coyotes.
