There are many solutions to the problem, and the best for a specific case depends on location, personal tastes, local regulations, and a variety of other factors.

In some situations, killing the grass is not permitted or undesirable and so moving the hives a few feet periodically onto a freshly mowed area of lawn works well, and lets the previously occupied patch recover.  The bees will find the hives with no issues if the move is only a few feet and the hives stay in the same relative positions to one another. 

That is what I do, personally, with my small operation.  Having a forklift makes it simple.  Not everyone has that option, but if the hives are worked from top to bottom from time to time, it is simple to move each floor onto fresh grass when reassembling the hive.  FWIW, we used to drop the hives onto their backs, so we could start with the bottom box and work up and not distrurb the same bees twice, as happens when working from top to bottom.

In other cases, killing the grass is permissable and frankly, for the small area being killed and no matter what alamists will have us believe, a herbicide is entirely harmless, but then you are working in a patch of dead vegetation or, eventually, mud.  

You might want to search the archives, though, for reference to bees getting agitated when the fields neaby were sprayed with Roundup.  We used Roundup on occasion and never saw any such probem, but, then, we were careful where and how we used it.  FWIW, entire sections (square miles) of land are sprayed with Roundup annually around where I live and it is no huge deal.  

Mulch, plastic, old carpet, tarpaper, silt screening, and any other material that will block out light will keep down grass.  Some are nicer to walk on than others.  Look around.  People are always throwing out carpet.  Mulch is nice, too, and clean.

We have to consider what kind of surface we want to work on.  I have had hives on sand, on gumbo, on weeds, on grass, on gravel, on carpet, and on mulch.  They all work, but some are nicer and cleaner than others.  Mud, manure, and sand are not things you want in your hives, and anything that is nearby is likely to get tracked, blown, or otherwise transferred into the hive, so that is something to think about, too.

I like my hives on live grass, and this year, although I have lots of pallets, I am using hive stands made from 2x4s on edge, separated by 16" pieces, like a ladder.  They are cheap and strong and can go up on cement blocks or be built with legs.  If they are up a foot or a foot and half, which is ideal from many perspectives, mowing underneath and trimming is easy.  Looks good, works well.

The problem with killing grass is that the ground eventually turns to mud or sand and later, when you move, there is an ugly patch that will go to weeds.

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