Irrigation pipe is typically 6-8" below ground and electrical should be at least 18" deep. Much more likely to dig up irrigation than electrical. I do wish I would have run a 110 circuit to my dock when I ran a 220 to my lake pump 35 years ago.
Running PVC or poly pipe? PVC must be blown out or drained each season in freezing climates, poly is less of an issue, it can sit with water, freeze and not burst. I hope your irrigation guy ran a hydraulic analysis on your pipe sizes. Inch and a quarter sounds small for such a large lot. But it depends on how big your pump is and how many zones you will run. I run my entire lot (15 heads) on one zone, 1.5 hp pump so I don't need any electric valves.