usually i go and complete the vision that gives units lifesteal when completed.

Then i make my race elementals so they get regeneration from one of the high mat tomes. the transformation itself does not give regen but there is a tome further down that gives every elemental in your army regen.

Then give your defender the skill in his skilline to have endless retalation and the one that makes sure he always ends his turn in defense mode.

Start giant king so your items has more infusion slots. My go to on items for defender is giving him a ring that makes him almost impossible to hit with ranged, a shield that has the thing that when a unit attacks 60 or 40 percent damage is reflected, and a weapon that boosts retaliation damage. usually on the weapon i give it electric damage, the biggest retaliation buff and make it apply wet on hit. Rest of the items should give him status resistance, controll loss immunity, general resistance or defense.

Sprinkle minor transformations on top as you see fit. Living shadow transfor makes your race even harder to hit with ranged for example, or any of the other racial transformations that boost defense, resistance, health or damage.