Make sure to have a berry/marker map as well as a Pokemon that knows teleport. (fly works just as well if you have the badge for it)
And if you hit any invisible walls along the way, just go around them.
Head east until you are above Route 210.
Head south until you are east of the Pal Park area.
Head west until you are in the Pal Park area.
Repeat 1W until you are just west of the Pal Park area.
Repeat 1S until your geographical indicator is 1 step from moving down from Route 221.
19E 17N. Save and SR.
When you need to leave, go outside the park, and use teleport.
Note that this is useless on an emulator unless you have a way to transfer generation 1, 2, and/or 3 Pokemon to generation 4.