Whether dropped or after hitting something?
I lost only one. Made it back sliding around like crazy (too lazy to take off my harness).
I have never lost a fin, but I had a finbox fail on Tiga board. Lots of smashed fins on the rocks though.
3 worn off fins due to shallow water.
From 23 to 18/19cm.
And one broke off at the fin screw due to a basalt block.
All usfinbox fins.
Blast from the past.
The first boards I made were thrusters. 3 deg toe in. Then using angled plastic fins ,reverse 2 deg to offset the toe in .
We had options back then of 0 ,1 ,2 ,3 deg side fins.They were there purely for the safety factor of being able to get home after snapping the centre fin. We were doing dangerously long runs. It was not because we were copying the cool wave riding guys. Although it did look cool. At the time ,we , (freeriders ,were all using those US box football fins. ( remember them ?) I think they were Australian made. And those other swept back versions. They were supposedly polycarbonate, but they weren't, cos they snapped at the base. They were the first fins you could push hard with the back foot. It was a time when rounded pintails were becoming groovy. Before wide boards were a thing. I think it was the start of the feeling of pushing a fin that allowed wide rear ends. Before the long pointer fin. That was also the time twin stringer blanks were good for holding the box. You could never roll a twin stringer box. Add another half a kg.
Those were the days.
Ps, oddly my favourite go to board now is a rounded pintail with wingers instead of cutouts.
Its going to be be the new thing again .
Yeah, probably not 
Have lost a couple. Lost one hitting kite lines a few years ago. Most recently hit a sandbank and lost one of the rear quads. Just got replacement yesterday in the post. Happy days.
Surprisingly very few ,all were either us boxed or single bolt power box. Never lost a Tuttle fin even when I hit the reef at Cervantes.
Over here in the Netherlands, none. We sail spots with sandbanks. But I do remember getting a bit too exited about the waves near the harbor wall in El M?dano (Tenerife), lightyears ago, didn't only lose the fin but also totaled the board. A week later, my then girlfriend came with a new board. I recall being so happy to see my new board, and she noticed... Not my proudest moment, but the new board and myself had a fantastic remainder of the holiday.
Lost no fins but I've shortened one on a turtle and rotated one in a tuttle box on a dugong. However I have lost two foils hitting sand banks.
Lost one and tried the harness dragging , one of my worst experiences, very hard on the arms and going almost nowhere
I've hit rocks and things many times but I've only lost 5 fins - 1 Tiga conic snapped at the root; 2 trim box fins broke at the front tab and fell out; 1 Tuttle snapped at the root (destroyed the box too); and I think the other was a power box. I haven't lost any for ages.
Yes, sailing back without a fin is a real exercise. You can practice it by sailing fin first.
I was doing one to two a year learning ,found a few diving and changed the grub screw,I now know where every rock is now ,
my worst fin that broke off level with the board ,i hit nothing just over powered ,just broke off for no reason ,it was 1 klm out to sea ,so much fun .getting back in 
lucky for me it was side shore wind ,i think i would rather tear a sail than loss a fin ,its the worst feeling .
wide boards are almost impossible to sail without one ,
Half a dozen hitting things, few more shearing off at the base, and a few more cracking out of their heads (thank you Select).
Select to expand quotepowersloshin said..
Lost one and tried the harness dragging , one of my worst experiences, very hard on the arms and going almost nowhere
Good news is that if you are a freestyle guy, you just flip the board around and sail back fin(less) first. Easier than if you had a fin!
Lost 4 - none due to hitting anything.
2 large weed fins just broke at the base when going upwind - slow going, big sails, a lot of foot pressure.(not a G10)
2 lost due to the thread being worn out. Just dropped off.
Lessons learned - only buying quality fins now, and making sure the bolt goes in all the way.
Three, all PB. One the bolt failed on a far side of a lake and i had a 2 or 3 k torture slog dragging my harness. That was the worst. Another i hit shallow rocks, but only about 200 m out, so slithered back in, that was the most fun. And finally coming down wind in through a long muddy shallow section at low tide i took fin out (had a bolt with a toggle) and shoved it in a foot strap and plowed back rather than walk, surprise surprise, it fell in the mud, that was obviously the stupidest.
Darn that's quite a bit then!
PB for me too, the fin wasn't in right. First time using the board, tight box.
A LOT.Usually snapping at the base though so I still have the bolts. Always seems to happen when you least want it to...
Managed to get a pic of the exact moment it happened once! 
I reckon if you went to New Cal or Feurteventura with a snorkel you could find some nice fins on the bottom.
Non, but I have lost a couple of fins when I've accidentally left them on top of the trailer, and driven off.
In recent years only one- hit a log going flat strap and it sheared off at the base. Bright side was for a few moments I thought it was a crocodile I'd hit- so the finless slog home seemed a trifle once I'd realised it was indeed just a log.
Further back- Ledge Point reefs are home to a large number of my fins (the reef is stronger than a fin- who would have thought?!) , and further back yet when I was using Tumiati fins in a Tiga Pro I came to the conclusion that the name was in sone dialect the word for " snap with zero loading, preferably way out the back". They were super cheap so I would just buy several at a time..So quite a few!
