Probably oil-based polyurethane. For not too much more, you could build one out of particle board and cover it with laminate. It would last longer than varnished plywood.

What do you mean by "wearing out?" Normally, wood surfaces should be maintained and re-finished, not rebuilt every few years. If the layers are coming apart, then it was either neglected, or is subject to heavier use than the material can handle. If that is the case, then maybe you should choose a different material.

The island in my kitchen is made out of laminate flooring and then covered in a two part apoxy and lots of it.Also, the scratches just buff out. We will continue it to the countertops next.
Could also be a varathane.

If the finish is very thick, it could be epoxy.

There is a fiberglass resin called 'Clear-Cast', which can be poured onto a surface at nearly any thickness. A lot of casual restaurants/bars make tables like that. You build a lip around the plywood to keep the resin in place while it cures. You can encapsulate decorative items under it, too. I don't know about scratches though- it will scratch w/ use. I guess you could buff it out once in a while.