I posted a picture and a description of how to use shockcord on your tarp guylines in that thread Ken posted the URL for earlier in this thread.
It looks like this...
...and works in this way. Stake out your tarp guyline as you would normally but stretch the shockcord out as you do until you are pulling the guyline itself taut. The shockcord will take up the slack when and if your tarp begins to sag due to moisture, rain etc.
"They are supposed to prevent your tarp from ripping in high winds letting the tarp have some give".
I don't remember ever hearing of this as a reason for using these types of guyline tensioners. ;-?
Ken mentioned two words, "projectile stake".
If there are large enough rocks available lay one over each of you stakes or on your guylines just in front of your stakes. You don't want to wind up looking like this guy.
As far as the high winds go, are you taking advantage of any natural windbreaks? Think leeward and windward sides of a peak, etc. Are you pitching the foot end of your tarp low and pointed into the prevailing wind direction?