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Off the yard is a slang variation of "off the chain", a play on words since off the chain references a dog that has been let loose, aka freedom from restraint.

"Off the yard" means that after you've gone off the chain you escaped the yard, hence the expression "off the yard".
Example #1:
Mom: Who let the dogs out? I don't see them anywhere.
Kid: He's gotten off the yard. I'll go look for him.

Example #2:
Guy: Man that party was off the chain!!!
Guy #2: Naw man that went past off the chain! That party was off the yard!!