I bought a nice metal arbor few years back & found that even tho it was heavy it was tipped over after a good wind. So I got some rebar, painted it forest green to match the arbor, pounded it in (Had to dig out some 1st as went down about ft & then pounded it in & filled holes back up, had green wire that matched & wired it on to arbor. Part sticking up above ground is about 2 1/2 ft. so probably 5 ft. rebar sunk in several places & either side of trellises would do it. Strongest wind we have had is 60 mph I think. if your's are stronger you might want rebar taller. Then if you no longer want it there you simply dig out the rebar & no damage done . Good Luck!

What about using wood Skids? You can always find them for free. Or wood shutters? I just saw on my local craigslist someone selling used ones for $1 each.