Upgrading Fence

Hello, right now I have a standard 54" high 5 wire high tensile fence running around a field to keep cattle in. However I would like to rotate that field this coming year from pasture and grow vegetables in it, the problem is I have very high deer pressure in my area.

My solution right now is to try to "extend" the fence upwards. I am going to try to lag bolt on a board or angle iron up to reach 8' high and drill holes in it and run another 3 strands of high tensile through it. I won't be able to put the high wire under much pressure for structural reasons with this, and I worry if a deer does jump it they would barrel right through it.

Anyone have any ideas on upgrading my current fence to keep deer out, or how to keep them from jumping if I do go with my current plan?

Thanks for the help everyone.

I would first try a baited electric wire before going to all the trouble of raising the physical fence. You would have to go 8 or even 10 feet to keep out deer reliably.
Get some plastic insulators and run a strand just above all of your other wires, or if that seems too high, get the ones that extend out a few inches from the posts and run the wire along the outside of the fence. Hang little tags of aluminum foil every few feet on this and bait them with a swatch of peanut butter or jelly or some such. Deer will smell this and give it a lick and get a really good shock! They won't be back for months!
Incidentally, I've used this same technique to get goats to respect single-wire fences, too....

I think that it is the sight of the fence, not its structural strength that deters the deer. Make it highly visible. Few, if any deer have PhD's in engineering, but they can all spot something that may impede their safe passage into the Garden of Eden.

In tough years, if there is nothing for them to eat outside the fence, nothing will stop them from trying. I know of people who have planted 'deer plots' well away from their garden areas, which seems to make both parties happy, as well as a well stocked freezer.