Dog safe pen/marker/dye to use on dog skin
I would like to monitor the size and shape of two cysts on my dog's back. To do this, I'm planning to shave the fur off around the cysts. I'd then like to use some sort of dog safe pen/chalk/marker, to mark the outline of the cyst, then take a photo of it with a ruler.
I saw OPAWZ has dog safe dye pens. Has anyone used these? Will these work on dog skin rather than fur? Or is there a better option that I should look into?
Additional info:
My dog is a light apricot color with light skin (cockapoo), so dyes should show up okay on him.
I'm not a pro groomer, but I do all my dog's grooming myself, so I can easily clip this area.
The cyst is the same color as my dog's skin, so that's why I need something to outline the edges for the photos/records.
Ideally, whatever dye/pen I use would wash off quickly, since I'd prefer not to have these outlines stick around, but it's not a deal breaker. I'll probably try to use a more neutral color in case the dye sticks around for awhile.
My dog's vet has already done fine needle aspiration of both cysts a year or so ago when they first showed up and determined there aren't any current concerns about them. One of the cysts seems to have grown a bit since then, so the vet did another fine needle aspiration and again determined that it's normal (confirmed by sending out to pathology), but I'm an anxious pet parent, so I'd like to have a more quantitative way of monitoring them.
Thank you!
Edit: I'd also prefer something that can be applied with a decent amount of precision, since the cysts are fairly small (around 0.5 in diameter).