I would recommend using new marbles. Vintage marbles will vary in size, slightly, so if you can deal with this, go ahead. So first, find your marbles if you’ve lost them, then determine a drill bit size that will bore a hole, ever so slightly smaller than your marble. You want it to press in snugly to help it stay put. No adhesive needed. I advise drilling test holes in scrap wood to help you get the right sized holes made. You may need to purchase a special sized bit.Further details at Garden Drama, via Neatorama.
I lose a marble or two over the winter from the wood contracting and expanding and maybe a couple over the summer, but a little vigilance, popping them back in is all that’s needed.