Walking bay?

we had a walking bay last week also. found where they crossed the river and it was a group of very large pigs. spent 7 hrs trying to close the distance. 300 yrds was as close as we got and i like my dogs too much to send them from that distance in thick brush. at the time we were mad as hell and wanted to trade our dogs for rougher stock. Has any one else found that your luck stopping hogs gets worse in the summer months. We caught pigs every time out when it was cool but as soon as the heat and foilage came on our luck turned for the worse. Not sure if its dog wise pigs or a change in conditions but it sure is frustrating.