Most Garmin and SportDOG systems come with both long probes and short probes. With other brands, it depends on the unit. We include them on the accessories list in each ecollar's description
so you'll know what you're getting.
As a general rule, dogs with short coats (English pointers, GSPs, Brittanys, beagles, hounds) use short probes, while dogs with longer, thicker coats (labs, goldens, and Chessies) may need the longer probes.
This can vary depending on the weather conditions and the thickness of the coat or undercoat of your dog.
Even with the longest probes installed, it may be necessary to thin your dog's coat. You do not have to shave him to bare skin, but inconsistent (unreliable) skin contact will result in inconsistent stimulation.
All ecollars need to be very snug to work. When fit properly, they are tighter than many inexperienced users are comfortable with. If the collar is too loose you have 2 problems -- inconsistent skin contact (see above), and they can rub causing serious skin irritation. The best way to fit an ecollar is high on the neck, just off to one side of the larynx, and very snug. If the collar is fit properly it should not move from this position, even on a very active dog.