A properly configured, mechanically sound machine running adequate feeds&speeds should not loose steps to begin with. I would primarely focus my attention on getting your machine operating properly. When that is done soft limits are quite capable as a fail safe for many scenarios.
Hard limit switches are also possible as a furhter barrier to chaos.
You could use a relay that control all power to the CNC, when tripped power is shut down completely, router and all.
But based on most of your postings recently I think you have a combination of issues, mechanical and feeds&speeds.
Xcarve anno 2015 you say:
Gshield? If so it is not able to provide enough current to your steppers to bring out their potensial. Especially on Y where two steppers share one inadequate driver.
There is also the chance of the drivers overheating which will cause sudden “pause in motion” for the troubled axis until its cooled down again.
If you are willing to lean on the experience of this forum, and make a specific thread for your machine, we may be able to help you. Show us your machine, share your GRBL parameters and feed rates in one place.
That makes it easier for us to help.