Safe, interactive dog toys?

Any safe, interactive toys I can give my dogs when I'm not home for a few hours? Something that can work their brain, but isn't hard to chew up? My terrier/chihuahua mix (who is more terrier than chihuahua) can chew up a red Kong toy, no problem. My terrier/Italian Greyhound(or Greyhound or Whippet)... show more Any safe, interactive toys I can give my dogs when I'm not home for a few hours? Something that can work their brain, but isn't hard to chew up? My terrier/chihuahua mix (who is more terrier than chihuahua) can chew up a red Kong toy, no problem. My terrier/Italian Greyhound(or Greyhound or Whippet) isn't a strong chewer, but is hyper all the time so I want something that can help her fatigue mentally. A price that isn't too high, but if it lasts as long as my dogs do, I don't mind.
Freezer friendly hopefully!
Right now, it's hot so they'll be kept indoors with a doggie door to go outside. I don't want anything too messy.
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