Ds is the same age and pretty uncooperativ if he doesn't want to go up. Even today i fought with him and got him into a quick ruck. Once he was back there, he knocked out. Have you tried a ruck tied under bum? Or maybe go for a little more length and do a ruck tied in front so you have those crosses under his legs if he tries to pop out of the carry.
Wife to DH and mommy to DD (12/07) and DS (2/11)