!/16th inch steel cable is almost invisible, yet very strong. Get some 1/16 cable clamps to secure one end into a loop,put it around or through whatever you are attempting to keep in place.
Figure out what part of your display item is the thickest-strongest and loop through there,then drive a stake into the ground to secure the "Earth" end of the project.
Make sure to check with local utilities first and they have usually up to three days to arrive and spray paint lines to mark phone, gas, electrical buried services.
In Illinois its called "Julie" , I think ?
For tombstones I use wood dowels running up the inside of the foam. For a few animatronic zombies I use wood bases under the clothing with holes which allow me to secure the props into the ground with tent stakes. I have one prop where I use stones, and a stand alone FCG I use a cast iron christmas tree holder covered in black fabric.
All of my foam tombstones have narrow PVC pipe inside of them, then I stake rebar into the ground and slide my tombstones over them... very windproof, as we get tons of wind. Props and fences (that are on hollow poles) also get slid over rebar that is staked into the ground. I have used tent stakes to pin fabrics on props down, too. Also, any props/decor that is near a railing or fence, for example, is zip tied to them.
Ditto what Witchy Kitty said goes for me too. Most of us learned the hard way as I still have visions of my window witch coming loose in a strong gust and flying down the street. I have to deal with wind all month long and tend to pick a warm calm day at the beginning of the month and spend more time bracing everything than I do most anything else. Rebar or threaded stakes for the tombstones. I tend to use the 6 foot threaded bars from Home Depot for my skellys and lifesize props, 3-4 foot if they're posed on the ground. They're a little cleaner, thinner and easier for me to work with when doing it myself . I go with the medium width for enough strength. I know most go with the rebar as it's cheaper. I'm not one for taking mine all apart like some of the more skilled people on here so for me the bar goes through the hip and ziptied to the front of the spine and resting securely under the chin. The cardboard shoulder type props get duct taped to protect them. (I learned that after having a prop's shoulders shred to mush in my rainy, windy October weather). Those type of props get a pvc pole slid over the metal rod into the neck or with a T connecter and 2 pipes on the sides to shoulder size if there's no hole through the head. I'm a little anal and if you can see it I will paint the bottom part black and the top bone colored for the skellys. Fishing line is my best friend. I then brace the rod with the fishing line to the cemetery fence or tent stakes and it has worked very well for me. Like Witchy if they have fabric I thread the fishing line through the fabric in spots to the tent stakes in the ground to make sure they don't turn. I make a mental note to avoid tripping myself anytime I walk into my cemetery though it has happened Helps with anyone that may think of helping themselves also as I tie everything down so if they are successful in getting it loose they'll probably trip on their way out. Other than the year of "Sandy" I've had pretty good luck with everything staying put throughout the month with no more than minor swaying of some on very windy days.