Ab wheel or hanging leg raises are about the only thing I would bother with.
In addition to the ab wheel and hanging leg raise, at the risk of sounding like a crossfitter, I also like L-pullups. They are brutal, and a recent bout left me more of a wreck than the ab wheel has in some time.
Dragon flies!
First of all, I would like to ask the reason for doing abs. As an assistance exercise or for aesthetic purposes? For assistance exercise you should start very low in volume (1 set) and intensity (BW x 10 Situps) and progressively increase every workout. There is no reason to start with a weight. The reason is to protect your progression on Squat and Deadlift. For aesthetic purposes you should drop bodyfat.
Yes my question was asked in regards to providing additional stability for the big lifts. As an older lifter I want to make sure I am doing everything possiy to avoid injury. I already focus diligently on form and contracting abs during my lifts. I might grab an ab wheel to try a few rollouts
You should get plenty of stability work with squats, deadlifts AND overhead presses. And if you do chins instead of rows you will find that your abs get worked, too. Rows just don't seem as useful as chin-ups.
Even if you can't do a single full chin-up yet, do negative chin-ups (starting from the top of the bar) with as many sets as needed to get 15 reps. Then try 8 sets of 2 negative chin-up reps, then 5 sets of 3 reps, then 4 sets of 4 reps, then 3 sets of 5 reps, then try 1 full chin-up, and 14/15 reps of negatives, then do 2 full chin-ups, etc. You get the idea.
In any case, the best way to achieve stability is by adding weight on the bar and trying your very best to maintain good form.