Take the power to create districts away from the legislature. Give it to a non-partisan commission. 1/3 Democrats, 1/3 Republicans, and 1/3 other/no party. We did that in California, and almost none of the legislators were happy with it, which means it probably did a good job. The state still wound up with mostly Democratic representation, but that's more a product of California being heavily Democrat. I'd imagine that if you did the same thing in Texas, even if the districts were much less gerrymandered, you'd still have mostly Republicans.