This morning most of the cattle were back on the sprayed field. Not exactly sure how they got there, but obviously my internal fencing is no longer adequate. Our guess is that Shauna, the one that a few years ago pushed through barb wire to be with some bulls, now realizes she can do it on any older fence and has lead the others through some weak spot. Of course, that might have happened last week, and now the rest have learned the same lesson.
I had tightened and realigned where they went through before (lots of tuffs of hair on barbs is a dead giveaway), but that was done via "kinking" - twisting the barb wire with pliers to form an "S" curve. Makes the fence feel tight to a casual observer, but a determined cow can press hard enough to straighten the S.
Choices now are all new internal fencing: either tight barb wire (cheap - $2/ft), woven wire (no worries of them ever pushing through $3/ft), or electric (cheapest - $0.50/ft, but relatively high maintenance). This is complicated by our desire to build the lake someday, which will flood out parts of existing and any new fencing. Note that we are talking about thousands of feet of fence if we redo it all, maybe 10's of thousands.