We have a wooden version of the nina ottosan toys and Prada and Gucci love it! it keeps them busy for a while although Chanel doesn't really care for it at all
They also like the kong toys you can stuff with treats, again that keeps them busy
If you can't take Ren out at the moment, then if you have the space you can play fetch for a while indoors. My 3 are generally lazy so after about 10 mins of chasing around a squeaky toy they sleep or lye down for a good while.

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If you want the best seat in the house, you've got to move the Chihuahuas!

Not to be a bad influence, but two is better than one!