Should I really train at Strongholds while people in my party AFK?

I don't know if this still works, but you could put them on Carrot Chairs so they're too high up for the mobs to hit.
Some friends and I did this back when SH was glitched and mobs wouldn't attack.

That doesn't work anymore at DH2. If he's training on Adv Knight As (I think the map is Knight's District 1 or 2?) there are AFK spots.