Are you afraid your SUP will be stolen from your car?

[SUStenance]

Yes.

After having a board stolen while on vacation, in an area I thought was safe, I have bought these:
http://www.homedepot.com/p/Keeper-9-ft-Locking-Cam-Buckle-2-Pack-07909/204062706?MERCH=RV-_-RV_homepage_rr-2-_-NA-_-204062706-_-N

Granted, even though the straps are steel reinforced, they could still be cut with a big enough cutter. I view it as a deterrent, enough to slow some one down. It will also give some peace of mind when stopping for grub, etc.

On next years vacation I will keep the board on one of the "upper decks" of the vacation house and use these to secure it to the deck.

There are more secure straps and locks (i.e., docks locks, etc.), but this should fit my need.

BTW, I did recover my board that was stolen and now have it in my possession as of yesterday  .

[supthecreek]

First of all SUStenance.... thanks for going away..... perfect waves since you left. Just like last time. 
Jimmy and I were talking about you in the lineup this morning (in between perfect sets) thanking you for being the sacrificial man out 

Super stoked that you have your board back... it was your Sherlock Holmes detective work that got it back.

[SUStenance]

Yes. Very grateful to have it back.. & You're more than welcome.. anything for my bros. I hope to make it home around midnight, then take a little "nap" and see y'all at DP tomorrow.

First of all SUStenance.... thanks for going away..... perfect waves since you left. Just like last time. 
Jimmy and I were talking about you in the lineup this morning (in between perfect sets) thanking you for being the sacrificial man out 

Super stoked that you have your board back... it was your Sherlock Holmes detective work that got it back.

[blueplanetsurf]

Yes, I'm afraid, it happens.

Dockslocks is another good option that was not been mentioned and it also works well for storing a board that is not on a roof rack.

http://blueplanetsurf.com/products/docks-locks-complete-kit