It's hard to make it illegal, because under the current system someone needs to draw the lines somewhere, and as long as they can reason why those lines are in those places, it's hard to prove malice.

Attempts to negate gerrymandering typically focus on making sure that those deciding the lines are as unbiased as possible, usually with cross-party committees drawing the lines instead of elected officials.

The best option though is to remove the need to draw the lines at all.

In theory a third party could spring up with the singular goal of fixing democracy by doing away with gerrymandering, instituting proportional representation, and removing overreaching executive powers and probably do well enough to get some movement towards those ends from the other parties if nothing else. They could all promise to resign and hold new elections once their goals are met and to not vote on anything else. Throw federally legalized pot in there if they really want to clinch support.