Too early to tell if this constitutes a recurrence. If the tests that were performed were sensitive to 0.1 then a minute change or even lab difference could show up as "detectable" 0.1. If it continues to rise, then you may need to explore salvage radiation. With your husband's stats it is very likely that if this indeed is a start of a trend, it would be a local recurrence that salvage radiation should take care of.
Take a deep breath and don't panic. This could be nothing, but even if it is something, you still have lots of options.
Father died from poorly differentiated PCa @ 78 - normal PSA and DRE
5 biopsies over 4 years negative while PSA going from 3.8 to 28
Dx Nov 2007, age 46, PSA 29, Gleason 4+4=8
Decided to participate in clinical trial at Duke - 6 rounds of chemo (Taxotere+Avastin)
PSA prior to treatment on 1/8/2008 is 33.90, bounced on 1/31/2008 to 38.20, and down at the end of the treatment (4/24/2008) to 20.60
RRP at Duke (Dr. Moul) on 6/16/2008, Gleason downgraded 4+3=7, T3a N0MX, focal extraprostatic extension, two small positive margins
PSA undetectable for 8 months, then 2/6/2009-0.10, 4/26/2009-0.17, 5/22/2009-0.20, 6/11/2009-0.27
Salvage IMRT + 6 Months ADT: Casodex started 6/12/2009, Lupron 6/22/2009, PSA 6/25/2009-0.1, T=516, 7/23/2009-<0.05, T<10, IMRT to start mid-Aug