Stump removal - Honey Fungus risk?

Moved into a property last year and have just had a row of 35ft Leylandii removed which was 'planted' in a raised bed 2ft off the ground. I was expecting to see a mass of large roots and poor dry soil under the shingle and membrane but to my surprise it was nice black crumbly soil, full of worms and not a root in sight. I have dug down 12 inches so far and am just coming to the top of the flare. So someone in their wisdom in the past buried these poor trees up past their ankles in soil, no wonder they were in such poor condition.
The question is what should i do with the stumps and whats the risk of honey fungus developing. I could hire a stump grinder or i could simply get out my chain saw and take them off as far as i can dig down, probably 16inches. If i did that, covered them in 16inches of soil and planted a yew hedge on top is there a risk of honey fungus from what remains of the stump? Any other ideas? I can really only work on 1 or 2 stumps at a time and move the soil along as i go covering the previous two i worked on. thanks