Mine buildings as if your playing Original Ren, without the added defenses. Then ignore the guy dynamiting your defenses.
Defenses are expendable. I suggest to use your time killing buildings, while your enemy wastes time killing your defenses. If you manage to get the War Factory or Bar, you have made it impossible for him to contnue this tactic, and he still has to get past your mines to do any real damage.
I do like the idea to create a delay while deploying. It would stop the hopping in and out at pillboxes, and make you bring some skill to plant without dying. ( The satchel delay would work for this in my opinion.)
and it wouldn't bother me to see dynamite count reduced to 1 on most chars, but probably isnt necessary if the delayed plant is implemented.