What is the meaning of "Lishmor Mezimos"?
R. Yonah: Yir'as Shamayim will be Aleihem 1 ; he will not cast the yoke off them.
Malbim: This corresponds to "l'Chachmasi Hakshivah" (1). Guard the Mezimos, i.e. the deep counsels of Chachmah.
It seems that the plural must apply the lips. However, why did R. Yonah say Aleihem (masculine)? Even if 'Safah' can be masculine (Radak Divrei ha'Yamim II, 4:3), but it is almost always feminine! (PF)
What is the meaning of "v'Da'as Sefasecha Yintzoru"?
R. Yonah: [He must guard his lips from] frivolity, which leads to Ervah (Avos 3:13). Zehirus is guarding from Peshi'ah, guarding thoughts from casting off the yoke, lest he be caught in "Nofes Titofenah" (3).
Malbim: This corresponds to "li'Svunasi Hat Aznecha" (1). Da'as corresponds to what one understands with clear Yedi'ah, via senses or proofs. Da'as is associated with the lips. Via Tevunah he will understand Binah until he comes to Da'as and clear knowledge that will guard Da'as.
