?:Need an English to Latin translation...

Mendacem veritem celare non potes.

Er, there's a bit of a typo there, bec. the Genitive of "veritas" is "veritatem" so the root for the other endings is "veritat-". And using the Accusative to render "from"?

Yup, should be veritatem, but it is the accusative, not genitive.

Normally celo is used with acc. of the thing concealed and acc. of the
person from whom it is concealed.
Ex. non enim te celavi sermonem (Cicero, Epistulae ad Familiares II)

Yup, should be veritatem, but it is the accusative, not genitive.

(slapping forehead) Right you are, George! Pecking out Latin translations at 2:19 in the a.m. is insane: it makes you fuse 2 thoughts (viz. "Genitive = veritatis, so stem is veritat-" with "the accusative is veritatem"), thereby typing nonsense. My apologies to Jess.