[Fiction question] (Warning: This one is a little yucky) How fast do bodies decompose?

[I tried to be nice and leave the gruesomeness out of the actual question, but the mod wants details, so there you are.]

How much decomposition happens in a three-month period to a body that is buried in rocky soil, in a moist, temperate climate, without any embalming?

The time period is from April to July. The body is that of a cocker spaniel, and it was just wrapped in a piece of cloth.

What condition is it going to be in if it is dug up?