Lyn and Tajsa are right - the submissive peeing usually occurs in a situation that is somewhat emotionally overwhelming for the dog. Common situations are meeting new people, getting scolded, having a loved one leave or come home, or being spoken to in a high-pitched, excited voice.
In this case, I think you probably just startled him when you grabbed his collar.Â
Maybe the next time you go to put the medicine in his eyes, maybe go to him and start off with a treat and some low key petting, so that he has a happy association with getting the meds. If you keep him busy with some peanut butter, he might not even notice you put the medicine in! Ranger does that all the time... "Mmm, peanut butter! Hey, how did my nails get so short??" Â
If you know that he has a pre-disposition to submissive peeing, just try to keep things like you leaving the house, and especially you returning to the house, real low key. Give him lots of chances to empty things out, even if he can normally hold it for awhile. I think you will find that he will probably eventually grow out of it...
You are doing just fine! Â