Do Heavy Ass Front Squats
This is why CrossFit people usually have that jacked looking core with bulging abs. They often are doing heavy cleans and front squats. Yes an assortment of other things but this is a tried and true tale to a stronger core.
Front Squats put the weight more forward which in turn forces more core engagement.
If you lose said engagement, the weight will simply pull you forward, collapsing you.
Keeping your elbows high and up, you automatically brace the core in order to keep the weight up.
Now yes, you can go lighter and do more reps, but this isn't going to produce the stimulus your core needs to get stronger quickly. This will create endurance, not strength.
(I'm also not saying soreness = Getting stronger. Topic for another day)
Lift Heavy, Eat Your Protein, Stay Hydrated.
Cheers Dorks