[Zeke]

I was one of the best you could find. I learned everything from the old timers that are now all dead. now, I'm the old timer. No one wants to learn from me. That's fine, as my better days are behind me. I actually can't equal my past quality anymore. But, I can remember how to do something right. Many times that's the old fashioned way.

You can't beat having your entire system holding the bench. Who knows what the depth and strength of the existing slab is? If benches were planned for that area, I would suggest that the plans would have called for some type of additional concrete or footing at their bases.

Also, be aware that the benches may need to be removed some day for whatever reason. Most of the methods suggested here would allow for that with little trouble. One of mine for slip-over posts would be more work.

A final idea is to purchase massive cast concrete benches, place them and forget them. Or, you could tack them down with some epoxy so they will never move sideways. No contractor needed.