This is a little too strong, but the idea is sound. What about this:
Sentinels

Artifact Creature -- Golem
1/1
Sunburst
Remove a +1/+1 counter from ~this~: put a 1/1 Myr artifact creature token into play for each +1/+1 counter on ~this~. At end of turn, sacrifice these tokens.
So the first time, you get four tokens. Then three, two, and so on. They're not "endless" anymore but that was the problem, really. Your version really wasn't that interesting, because it basically was just an artifact Moat - the opponent would only attack with flyers, and youd get tokens and then lose them to no effect. There's a lot more interesting things you can do with 1/1 tokens, especially fi they last until end of turn and not end of combat. Plus you can keep charging my version up.