The Fort wasn't really known about until 1922 when it was described in a Chalmer-Jervise Prize Essay of the Society of Antiquaries of Scotland written by a certain R.R. Boog Watson.

In this essay he describes how the Fort was discovered and the early excavations that were made. It also includes a reasonable map of the site.

Click on the map for a larger view.

Excerpt from the Boog Watson essay

Viewed from the west, Deuchny Hill has the appearance of a
truncated cone, but from south or north it is elongated, and consists
of three well-defined heights rising in level from the west end.
    Both to the north and south are swampy
hollows, beyond which the ground again rises, but nowhere attains
the height of the eastmost top.

This height commands a very extensive outlook: eastwards, the Carse of
Gowrie and as far as the Bell Rock light; southwards, from St Andrews
Bay and over Fifeshire; westwards, .Strathearn and to about Tyndrum;
northwards, the valley of the Tay, Strathmore, and the Grampians.

Only to the north-east is the view cut off by Murrayshall Hill. So prominent
is the site that it was selected for the Peace Celebrations bonfire,
and it was this circumstance which redirected my attention to it. I had
at an earlier time noticed what seemed to be traces of a wall, but
having examined the Ordnance Survey Maps and finding no indication of
any site, I had concluded that either I was mistaken or the remains
were quite modern.

When, however, a small stone mortar was brought to
the Perth Museum as having been found on the site of the bonfire, I was
led to re-examine the site

If you want to read more the full essay can be viewed here.