Slindon Estate Yard Saw Pit.

The old estate yard at Slindon has many interesting features; it would have been at one time a hive of activity, with carpenters, blacksmiths, all working at there trades supplying the needs of the great house and the estate in general.
Now this has gone, but there are reminders left of this bygone age, one in particular is the saw pit, here wood felled on the estate would be brought to be sawn into planks for various uses, it would have been hard work sawing often massive timbers into planks, and the worse job would have been at the bottom of the pit, for all the saw dust would fall upon you, and the hardest work, for you had to pull the massive saw on the downward stroke, the top man keeping a straight cut.
The saw pit at Slindon will be fully excavated later this year.

Notes.
'Top dog' is synonymous with the similar, if now archaic, phrases, 'upper dog' and 'over dog'. Clearly it is also the antonym of 'under dog' (now usually spelled as a single word) and its synonym, 'bottom dog'.
We have here a golden opportunity for those who consider plausibility to be enough evidence to hang a phrase derivation on. When wooden planks were sawed by hand, two men did the job using a two-handed saw. The senior man took the top handle, standing on the wood, and the junior took the bottom - in the saw-pit below. Add to this the fact that the irons that were used to secure the wood were called dogs and that the bottom position was much the more uncomfortable, and we can jump from this scene to the origin of 'top dog' and 'underdog'.
That may be true. The problem with it as an explanation is that no one has found evidence to back it up. There are printed references to saw-pits and to this form of work, going back to the early 15th century in England and the 19th century in America. None of these have any mention of 'top dog' or 'under dog'. Hardly likely that everyone, including Shakespeare, who referred to saw-pits in The Merry Wives of Windsor, would have ignored these colourful phrases, had they been in use at the time. For example, this extract from the 1876 Yale Review describes saw-pits in some detail makes no mention of 'top dog':
"The saw-pit was a rude structure about seven feet high, made of strong posts set in the ground wide enough apart to hold one or two pieces of heavy pine timber, and the sawyers, one above and one beneath, sawed out one hundred feet per day."
In fact t here are no known references to 'top dog' or 'under dog' in the context of wood sawing until well after the practise was superseded by mechanical sawing.
There are printed references to these terms going back to the days that the pits were still in use, but these all refer to fights of some sort, particularly dog fights. Here's a piece, for which the word doggerel might have been invented, that appeared in several US newspapers in 1859, under the name of 'David Barker':
The Under Dog In The Fight
I know that the world, the great big world,
From the peasant up to the king,
Has a different tale from the tale I tell,
And a different song to sing.
But for me - and I care not a single fig
If they say I am wrong or right wrong,
I shall always go for the weaker dog,
For the under dog in the fight.
I know that the world, that the great big world,
Will never a moment stop.
To see which dog may be in the fault,
But will shout for the dog on top.
But for me I shall never pause to ask
Which dog may be in the right
For my heart will hear, while it beats at all.
For the under dog in the fight.
Perchance what I've said I had better not said,
Or 'there better I had said it incog.
But with my heart and with glass filled up to the brim
Here's health to the bottom dog.