The fastest way to get all of these is by starting the course like normal then changing the mode to practice. I labeled which hole each secret hole is on so just go to that one, put on the stroke counter to 100, and time as needed.

If you need all the secret obejcts, Gattsta has already made a guide for this. https://steamproxy-script.pipiskins.com/sharedfiles/filedetails/?id=3022903215

The secret for Grassland is on hole 15. Take a decently powerful shot to the left and after a few tries, you should be able to make it into the barrel.

The secret for Winterland is on hole 18. Aim for the chest to the left with a bit of power and it should go straight in.

The secret for Mines is on hole 8. You can either shoot your ball off the halfpipe for it or hit the wood panel laying diagonally to the left of where you start the hole. (You can see this piece of wood in the picture)

The Graveyard secret is on hole 18. The hole alignment is right under the pair of eyes to the right of the pot with the portal where you start at. Make sure to have a lot of power on this shot because it is decently far away.

The secret for Pirates Cove is on hole 13. After shooting out the cannon, use a lot of power on the ramp to make it into the barrel behind the wood hut. This one is very tricky so it will take a few tries.

The secret for Jade Temple is on hole 13. Its pretty simple to get but hidden behind some bushes. It is in the bowl of the left of the screenshot in case you didn't see if at first.

The secret for VR Classic is on hole 7. All you have to do is aim to the left of the tee where you start and make it through the window. I recommend hitting the wall to the left side then having it hit on the base of the window so it bounces neatly into the pot.

Deep Blue is probably the toughest to find as it's not really hidden but you may not realize it's something that triggers as a hole. The crystal on level 10 under the pagoda is the secret hole for deep blue. You shouldn't have to hit too hard off the ramp since the gravity is a little lower in the water. You don't have to have an exact direct hit but should be around it. If close enough, it will drag the ball to hit the crystal.

I really hope this helped for anyone who was struggling to find one or just wanted to get all of the achievements. Anyways, if this helped, feel free to rate up and favorite as I will be updating this if there are more secret holes being added. Have a great day! If you have any questions, feel free to ask as I will be answering them in the comments.