Are there any toys that he responds to? The dogs I know all have some noise that they recognize and respond to more strongly than the voices of their owners. When my dog gets out, this (relatively) low-pitched squeaker from a toy he demolished does the trick. My aunt's dog, it's a bellhop bell. My other aunt's dog, a whistle. If there's something like that, you and your mom would do well to bring it with you wherever you go looking.
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