This answer is more technical than people are giving it credit.
Dogs can smell the tiniest microscopic particles from your weed, these particles get onto the outside of your container that you store your bud into, because they transfer easily from the oils on your skin.
The dog alerts because he can smell the tiny microscopic particles on the outside of your container that you've chosen to store your weed in after loading a bowl with your friends.
To prevent this transfer of microscopic material you'll need to start with a sterile container at your home.
IMPORTANT! DO NOT take your jar out of the package, until you've washed your hands, and are wearing gloves.
You'll take your bag or whatever else you've decided to put your marijuana into, and lay on to the counter top.
Now wash your hands well....
Put on a new pair of latex gloves, take your bag of weed off the counter, and drop it into the container. (I prefer brand new glass mason jars) Be very careful to not allow the bag of weed to come in contact with the outside or lid of the glass container.
Take off your gloves, and if desired wash hands again... I always do... better safe than sorry.
Take your brand new lid and tightly apply the lid. Now this container is sterile and ready for safe transport.
Now... Marijuana permeates any container with pores, which is pretty much every material known to man, so don't leave container sealed like this for more than eight hours for added security benefits.
A dog simply cannot pickup on this, as there is absolutely no marijuana particles for the dog to smell...
The only worries you'll have is find a good stash spot for the mason jar. Have fun at the festival!
rep goes along way...
I like the vacuum seal, but after you try that put in in a glass canning jar with a new lid and wash the outside really good. Haven't tried it, but glass will keep the smell inside.
Kind of like this but you'll need to ensure hand washing and gloves to ensure a fail-proof seal.