need tips on shaving a bun who's shedding fur

I used to dry comb them when they are in fur shedding season. It works in the past many years, until the other week, when 1 of my buns have a lot of fur, and it took me 20 min. or so to dry comb him, and he got really stressed from it

so I bought a fur clipper for exotic pet. Now my question is, how do you know where to shave? I can tell in some area that the fur is shedding, and I can shave that area, but in some other area, it's not that obvious.

any tips?

Have you tried damp hands as this method is safe but you must be careful using clippers as you don't want to cut the rabbit's skin.

I use the wet hand trick in the old days. It kind of work. I have a bowl of water, I wet my hand on it, and I wet comb my bun. Because of the large amt. of fur that they shed, the bowl of water quickly becomes fur mix, so I have to let my bun go, get rid of that bowl of water / mix fur, and get a new bowl of water.

Now, I have to chase my bun to finish off the job. But a 2nd bowl may not be enough, I could need a 3rd bowl

What sort of rabbit is it? Unless the fur is really matted that might not be the best idea. Angoras and fine coated lion heads get matted right against the skin and combing gets very uncomfortable for them so shaving is a good option. Also you need to think about how cold it is outside, will they be left with enough fur to stay warm? I only shave chests and bottoms in the winter and then only on the real fluffies if they get badly matted.
But there are times when clipping is a good option, and not just for woolies. Some lops have ridiculously dense fur and seem to end up wearing several layers at once. If this happens to a rabbit with weak skin then shaving can be the best option as a comb can tear the skin. (Btw treating regularly with ivermectin can improve this skin condition. I am convinced fur mites are involved.
And of course rabbits prone to mucky bottoms are best kept shaved underneath.
But routine shaving for a normal rabbit is not a good alternative to combing.

I probably wouldn't clip any fur unless it's matted/mucky. Clipping is usually more stressful than regular grooming. If you are going to clip never clip their feet.
Have you tried Zoom Grooms by Kong? I have used them on cats and they are amazing for when they're molting!

it's a mini Rex. What's Zoom Grooms? my buns lives indoor, hopping around the house, so the thickness of their fur doesn't make much different