MWM, I think you are being way too hard on this poster. This is intended to be a soft place to land for battle weary parents.
I dont know how on earth anyone on here can make the leap that because he and his SO live together means he isnt divorced. Heck maybe he is a widower or *gasp* never married before to his kids mother. And really does it matter whether he is divorced or not? I had one child going into my current relationship - I was still married when I met him. We had one other child and I was pregnant with the third before my divorce finally came through. There has never been any case where my oldest child was treated any differently than his brothers. It didnt matter who was handling what...Dad was Dad and I was mom.
Now I can understand that there is a difference in a 2 and a half year old and a child that was 10 when this poster moved in with him. I am gonna lay money on the fact that these kids probably knew the poster before he showed up at the door with his bags packed and two kids in tow.
Because I have no clue how old this posters own children are I wouldnt even consider commenting on his decision to spank. Or even when he did it. I find it very hard to believe that there are many parents out there who havent swatted a hand or butt at some time in their lives. I have no clue how anyone teaches a toddler not to touch things they shouldnt without giving the hand a swat and telling them NO firmly at the same time. If that is abusive then most of America should be convicted.
To the original poster, I do think you are up against a very difficult child. I had one that didnt punish well at all. Like your's appears, mine wouldnt do groundings. He left when our backs were turned. You have to get inventive and found out what his currency is. Everyone has some type of currency. We go to work to earn money, we have a hobby because it brings us enjoyment. You have to figure out what makes this boy tick. If he is so into taking things apart and then trying to put them back together again, well how about checking to find out if you can find old TV's, radio's and even bikes that are being tossed in the trash. Let him go to town on those things. I had one son who took apart everything and tried to put it back together again. He wasnt trying to do something wrong, he wanted to know how things worked. We got him broken things and he learned to make one good thing out of lots of broken things. He eventually learned how to build his own computers. Maybe your boy would learn to make awesome bikes out of parts and pieces he takes off old broken bikes. You just never know.
I also think if your kids are all old enough, a chart with the house rules and what the consequences are if broken is a great idea. I would have all the kids involved in making the chart though. This makes it much easier for a parent to take the anger out of infractions. You just point at the chart and they know what the consequence is and they also know they had a hand in deciding what that consequence will be. Of course a difficult child is going to take more time for this to grab a hold of but even special needs kids do have to learn there are rules in life and what happens if they dont follow them.
*Good luck.