Off-topic but perhaps interesting:

That's what they do when performing catheter ablation (a medical procedure for curing cardiac fibrilation by destroying minute parts of muscle with electric current).

DC would work just as fine on this procedure, but due to electrolysis of water, oxygen and hydrogen bubbles would form, which could get stuck somewhere. Using a square wave AC quickly reverses the reaction every period, like you suggested for the moisture meter.

https://en.wikipedia.org/wiki/Catheter_ablation#Technique

I don't know the answer to your question, but it would be worth trying.