What is "mi'Sod Mere'im"?
Radak: A gathering of evildoers. The same applies to "Lo Yashavti v'Sod Mesachakim" (Yirmeyah 15:17). A gathering is called Sod, because people who have a secret and a counsel gather; each tells his secret and counsel, and they reach a common conclusion.
Malbim: It is what they plot against me covertly.
What is "mi'Rigshas Po'alei Aven"?
Rashi: They are excited to find capital accusations against me - "Hargishu Al Malka..." (Daniel 6:7).
Radak: It is from a multitude [of evildoers]. The Targum of "v'Hishbati Es Hamon Egypt" (Yechezkel 30:10) is v'Avtil Yas Isregushas Egypt.
Malbim: [Hide me also] from what they gather openly with excitement and rebellion.