1)
Why does it say "Lo Ekach mi'Beischa Far"?
1.
Rashi: The ox is not yours - it is Mine!
2.
Radak: If I needed Olos, I would not take them from you. Everything is Mine, and in My Reshus! It mentions an ox, the biggest Korban, and Atudim, the big goats.
3.
Malbim: Do I need specifically the ox in your house, or the goat in your pen?!
2)
What is "Michle'osecha"?
1.
Rashi: It is a pen for flocks, like "Gazar mi'Michlah Tzon" (Chabakuk 3:17). Radak - the Hei is switched to an Aleph. The flock is Nichla (incarcerated) there.