This is why I'm closely following Pennsylvania's plan to award electoral votes by congressional district instead of "winner takes all". If passed, it would mean that vote-fraud in Philly would only affect Philly's electoral votes (which the Dem would get regardless), rather than throwing the whole state to the Dem.
Wisconsin, Michigan, and other states with large Dem cities should follow suit.
I think apportioning EVs by congressional district is a good idea, for the very fact that you mentioned - it isolates voter fraud, usually to the districts where the dems would win anyway.
Someone on FR equated this with the National Popular Vote movement and opposed it greatly, but in reality, it is the EXACT OPPOSITE of the NPV.