Guitar/bass plays this in dropped-D tuning (DADGBE):
   /   /   /   /        /   /   /      /
|--------------------|-----------------------|
|--------------------|-----------------------|
|--------------------|-----------------------|
|--0---0---0---------|--0---0---0------------|
|--0---0---0---------|--0---0---0------------|
|--0---0---0---3--5--|--0---0---0---6--5--3--|
   Dm                   Dm

and Dave plays this bass line during the beginning:
   /       /    /       /
|-----------------------------------|
|-----------------------------------|
|-----------------------------------|
|-------10-10---10------12------10--|
|-----9-------9----9----------9-----|
|--10----------------10----10-------|
   Dm

   /      /    /    /
|------------------------------|
|------------------------------|
|------------------------------|
|------10-10---10---9/10-9/10--|
|-----9------9------8/-9-8/-9--|
|--10---------------9/10-9/10--|
   Dm

Verse 1:
Dm
Rock on my belly, lying on the bottom of the pool
      Dm
I'm a rock on the belly, lying on the bottom of the pool

          Dm
There's a man on the bank ten thousand years my younger
        Dm
I see a face on the water one hundred, hundred
   years my younger

      F     Dm Dm       F     Dm Dm
|-----5-----5--7--------5-----5--7----|
|-----6-----6--6--------6-----6--6----|
|-----5-----7--7--------5-----7--7----|
|-----7-----7--7--------7-----7--7----|
|-----8-----5--5--------8-----5--5----|
|-------------------------------------|
But I can't go back, he can't go back

   F             Dm   Dm Bb
|--5-------------5----7--1--------------|
|--6-------------6----6--3--------------|
|--5-------------7----7--3--------------|
|--7-------------7----7--3--------------|
|--8-------------5----5--1--------------|
|---------------------------------------|
 I can't make it back to where I came
     C                  Dm
As I hold my whole body under


Verse 2:
Legs, tail, and belly shaking the top of the pool
Legs, tail, and belly shattering the window of the pool

Mouth and belly scaring the fish down under
Tongue and belly scaring the snakes there too


But I can't go back - the dog won't go back
He won't run the path to his master's home
'Til he climbs that bank over yonder


Dm with bass riff throughout the rest of the lyrics

Well, the fish gonna make it home in a couple of days
The birds gonna make it home before his grip turns dry

Everybody's moving but me
Everybody's moving but me
I'm gonna make it home piece by piece
(x2)

There goes my arms *make it home*
There goes my legs *make it home*
There goes my leadbelly

I'm a rock on my belly lying in the bottom of a pool
Rock on my belly lying in the bottom of a pool
Rock on my belly (x4)
Rock on my belly lying in the bottom of a pool

end on Dm > Bb > C > Dm (i.e. "I can't go back...")