please help! i have 2 chi hua huas.....

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i have 2 chi hua huas who are about 6 months old now, got them when they are about 3 months plus. i have been toilet training them using pee trays ( yes i bought 3!!) odour remover solution for "mistakes", treats and a big play pen for them.

i have successful trained 1 puppy, (both are brothers/best friends), he always pees & poos on the pee tray but the other always pees elsewhere! he always pees at the doggy bed & even his toys! i have washed them with odour remover many times & even threw away the stained toys!

can anyone tell me why the other puppy refused to be trained? they are both smart dogs and i am sure they know where to pee by now. i always give treats & lots of praises whenever they pee at the urine tray but the other puppy always refused to pee at the tray. i have bought them the largest pee tray so that it can fill 50% of the playpen, 50% is the bed & toys. i even bought a smaller tray for the other puppy so 75% of the play pen is filled with pee trays BUT still doesn't work! please help, i am going crazy cleaning up after the other puppy!!