G92 and M99 code uses?

hey everyone. I have been playing around with cncpro to figure out
more of its features so I can use them if needed. I have been trying
to figure out the "loop" L code with little luck. I have "V" variable
down pretty good and am starting to understand subroutines. In my
attempt to figure out machine coordinates (G54-G58) to make multiple
parts, I figured out a different way to make the machine do the same
thing over and over again by using G92 and M99! And here is where my
question comes.. HOW do I STOP M99 (rewind G-code and repeat)? For
example lets say I want to drill 50 holes 1 mm apart...I would now
write a G-Code this way:

G81 R.50 Z-5 (single drilling with .50 raise and drilling 5 mm in)
G80 (cancel drilling)
G00 X1 (moving X axis 1 mm over)
G92 X0 (This is the catch! RESETS the machine back to zero)
M99 (rewind and repeat)

The problem is I don't know how to stop the M99 code and if left the
machine would keep doing this sequence until it burns out :) How
would I specify it to do the 50 holes in this example?

One could also make the code more complex! Lets say you wanted to cut
a bunch of little squares 5 mm apart in a row. G-Code could look:

G00 Z-1
G00 X2
G00 Y2
GOO X0
G00 Y0
G00 Z.5
G00 X7
G92 X0Y0
M99

Hope this sparked some ideas! I am learning! What fun!!!
tauseef